How to split a string in oracle into variables based on the separator?


Say to split the below string into 4 variables based on the separator  :

l_string : = ‘AAAA:BBBB:CCCC:DDDD’;

  • l_var1:= ‘AAAA’;
  • l_var2:= ’BBBB’;
  • l_var3:= ‘CCCC’;
  • l_var4:= ’DDDD’;

Script:

DECLARE
  l_string VARCHAR2(100) := 'AAAA:BBBB:CCCC:DDDD';
  l_var1   VARCHAR2(240);
  l_var2   VARCHAR2(240);
  l_var3   VARCHAR2(240);
  l_var4   VARCHAR2(240);
BEGIN
  SELECT trim('"'
  FROM regexp_substr(l_string,'".*?"|[^:]+',1,1)) Col1,
    trim('"'
  FROM regexp_substr(l_string,'".*?"|[^:]+',1,2)) Col2,
    trim('"'
  FROM regexp_substr(l_string,'".*?"|[^:]+',1,3)) Col3,
    trim('"'
  FROM regexp_substr(l_string,'".*?"|[^:]+',1,4)) Col4
  INTO l_var1 ,
    l_var2 ,
    l_var3 ,
    l_var4
  FROM dual ;
  dbms_output.put_line('Var1 : ' ||l_var1);
  dbms_output.put_line('Var2 : ' ||l_var2);
  dbms_output.put_line('Var3 : ' ||l_var3);
  dbms_output.put_line('Var4 : ' ||l_var4);
END;
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Playing with Dates in Oracle!


In and around Oracle Application, as a developer you need to play with Dates while writing your code. Playing with dates is fun, although sometimes we faced some challenging tasks. Therefore it is always helpful to go through this feature of Oracle in detail. I did the same and here is what I have found.

Oracle database stores dates in an internal numeric format, representing the century, year, month, day, hours, minutes, and seconds. The default display and input format for any date is DD-MON-YY. Valid Oracle dates are between January 1, 4712 B.C. and December 31, 9999 A.D.

Unlike other datatypes, DATE datatypes are bit complex. However, Oracle Database and PL/SQL provide a set of true date and time datatypes that store both date and time information in a standard internal format, and they also have an extensive set of built-in functions for manipulating the date and time.

Get the current date and time:

Often it is required to retrieve the current date and time in our code and use them. Many developers go with SYSDATE function, but Oracle Database now offers several other functions as well.

SELECT SYSDATE FROM DUAL;
--27-FEB-12 (You will get the DATE from Oracle Database Server)
SELECT CURRENT_DATE FROM DUAL;
--27-FEB-12 (You will get the Current DATE from Oracle Session Time Zone)
SELECT LOCALTIMESTAMP FROM DUAL;
--27-FEB-12 01.16.42.486809000 AM (You will get the TIMESTAMP from Oracle Session Time Zone)
SELECT SYSTIMESTAMP FROM DUAL;
--27-FEB-12 01.19.41.059413000 AM -06:00 (You will get the TIMESTAMP WITH TIME ZONE from Oracle Database Server)
SELECT CURRENT_TIMESTAMP FROM DUAL;
--27-FEB-12 01.20.57.839733000 AM AMERICA/CHICAGO (You will get the TIMESTAMP WITH TIME ZONE from Oracle Session Time Zone)

DATE Format:

When a DATE value is displayed, Oracle must first convert that value from the special internal format to a printable string. The conversion is done by a function TO_CHAR, according to a DATE format. Oracle’s default format for DATE is “DD-MON-YY”. Whenever a DATE value is displayed, Oracle will call TO_CHAR automatically with the default DATE format. However, you may override the default behavior by calling TO_CHAR explicitly with your own DATE format.

Guidelines

  • The format model must be enclosed in single quotation marks and is case sensitive.
  • The format model can include any valid date format element. Be sure to separate the date value from the format model by a comma.
  • The names of days and months in the output are automatically padded with blanks.
  • To remove padded blanks or to suppress leading zeros, use the fill mode fm element.

Parameter

Explanation

YEAR Year, spelled out
YYYY 4-digit year
YYY
YY
Y
Last 3, 2, or 1 digit(s) of year.
IYY
IY
I
Last 3, 2, or 1 digit(s) of ISO year.
IYYY 4-digit year based on the ISO standard
Q Quarter of year (1, 2, 3, 4; JAN-MAR = 1).
MM Month (01-12; JAN = 01).
MON Abbreviated name of month.
MONTH Name of month, padded with blanks to length of 9 characters.
RM Roman numeral month (I-XII; JAN = I).
WW Week of year (1-53) where week 1 starts on the first day of the year and continues to the seventh day of the year.
W Week of month (1-5) where week 1 starts on the first day of the month and ends on the seventh.
IW Week of year (1-52 or 1-53) based on the ISO standard.
D Day of week (1-7).
DAY Name of day.
DD Day of month (1-31).
DDD Day of year (1-366).
DY Abbreviated name of day.
J Julian day; the number of days since January 1, 4712 BC.
HH Hour of day (1-12).
HH12 Hour of day (1-12).
HH24 Hour of day (0-23).
MI Minute (0-59).
SS Second (0-59).
SSSSS Seconds past midnight (0-86399).
FF Fractional seconds.

Examples:

SELECT TO_CHAR(SYSDATE, 'yyyy/mm/dd') FROM DUAL; -- Returns 2012/02/27
SELECT TO_CHAR(SYSDATE, 'Month DD, YYYY') FROM DUAL; -- Returns February  27, 2012
SELECT TO_CHAR(SYSDATE, 'FMMonth DD, YYYY') FROM DUAL; -- Returns February 27, 2012
SELECT TO_CHAR(SYSDATE, 'MON DDth, YYYY') FROM DUAL; -- Returns FEB 27TH, 2012
SELECT TO_CHAR(SYSDATE, 'FMMON DDth, YYYY') FROM DUAL; -- Returns FEB 27TH, 2012
SELECT TO_CHAR(SYSDATE, 'FMMonth DD, YYYY') FROM DUAL; -- Returns February 27, 2012
SELECT TO_CHAR(SYSDATE, 'FMDay, DDth Month YYYY') FROM DUAL; -- Returns Monday, 27TH February 2012
SELECT TO_CHAR(SYSDATE, 'YYYY-MM-DD HH24:MI:SS') FROM DUAL; -- Returns 2012-02-27 02:05:59
SELECT TO_CHAR(SYSDATE, 'FMDdspth "of" Month YYYY FMHH:MI:SS AM') FROM DUAL; -- Returns Twenty-Seventh of February 2012 02:06:36 AM
SELECT TO_CHAR(SYSDATE, 'FMDay, DDth Month YYYY','NLS_DATE_LANGUAGE=Spanish') FROM DUAL; -- Returns Lunes, 27TH Febrero 2012
SELECT TO_CHAR(SYSDATE, 'Day') TODAY_EN,
TO_CHAR(sysdate, 'Day', 'nls_date_language=Dutch') TODAY_DT
FROM DUAL; -- Returns Monday   	Maandag

TO_DATE & TO_TIMESTAMP Functions:

TO_DATE function converts a character string representing a date to a date value according to the fmt specified. If fmt is omitted, the format is DD-MON-YY. The nlsparams parameter has the same purpose in this function as in the TO_CHAR function for date conversion.

TO_DATE(char,[fmt],[nlsparams])

The DD-MON-YY format is usually used to insert a date value. If a date must be entered in a format other than the default format, for example, with another century, or a specific time, you must use the TO_DATE function.

Examples:

SELECT TO_DATE('2012/02/27', 'yyyy/mm/dd') FROM DUAL;
SELECT TO_DATE('022712', 'MMDDYY') FROM DUAL;
SELECT TO_DATE('20120227', 'yyyymmdd') FROM DUAL;
SELECT TO_DATE('February 27, 2012, 04:00 P.M.','Month dd, YYYY, HH:MI A.M.')FROM DUAL;

Similarly TO_TIMESTAMP used to convert char of CHAR, VARCHAR2, NCHAR, or NVARCHAR2 datatype to a value of TIMESTAMP datatype.

Examples:

SELECT TO_TIMESTAMP('2012/FEB/27 04:12:34', 'YYYY/MON/DD HH:MI:SS') FROM DUAL;
SELECT TO_TIMESTAMP('February 27, 2012, 04:12:34 P.M.','Month dd, YYYY, HH:MI:SS A.M.')FROM DUAL;
SELECT TO_TIMESTAMP ('27-Feb-12 04:12:34.123000', 'DD-Mon-RR HH24:MI:SS.FF') FROM DUAL;

Arithmetic with Dates:

Here are 3 golden roles:

  1. You can compare DATE values using the standard comparison operators such as =, !=, >, etc.
  2. You can subtract two DATE values, and the result is a FLOAT which is the number of days between the two DATE values. In general, the result may contain a fraction because DATE also has a time component. For obvious reasons, adding, multiplying, and dividing two DATE values are not allowed.
  3. You can add and subtract constants to and from a DATE value, and these numbers will be interpreted as numbers of days. For example, SYSDATE+1 will be tomorrow. You cannot multiply or divide DATE values.

Date Functions:

Date functions operate on Oracle dates. All date functions return a value of DATE data type except MONTHS_BETWEEN, which returns a numeric value.

• MONTHS_BETWEEN (date1, date2):

This function returns the number of months between date1 and date2. The result can be positive or negative. If date1 is later than date2, the result is positive; if date1 is earlier than date2, the result is negative. The noninteger part of the result represents a portion of the month.

• ADD_MONTHS(date, n):

This function adds n number of calendar months to date. The value of n must be an integer and can be negative.

• NEXT_DAY(date, ‘char’):

This function finds the date of the next specified day of the week (‘char’) following date. The value of char may be a number representing a day or a character string.

• LAST_DAY(date):

This function finds the date of the last day of the month that contains date.

• ROUND(date[,’fmt’]):

This function returns date rounded to the unit specified by the format model fmt. If the format model fmt is omitted, date is rounded to the nearest day.

• TRUNC(date[, ‘fmt’]):

This function returns date with the time portion of the day truncated to the unit specified by the format model fmt. If the format model fmt is omitted, date is truncated to the nearest day.

Examples:

SELECT SYSTIMESTAMP FROM DUAL;  --Returns 27-FEB-12 05.16.41.676947000 AM -06:00
SELECT MONTHS_BETWEEN(SYSDATE , TO_DATE('01-JAN-2012','DD-MON-YYYY')) FROM DUAL; --Returns months between Sysdate and '01-JAN-2012' (1.84580906511350059737156511350059737157)
SELECT ADD_MONTHS (SYSDATE, 1) FROM DUAL; -- Move ahead one month (27-MAR-12)
SELECT ADD_MONTHS (SYSDATE, -4) FROM DUAL; -- Move backward four months (27-OCT-11)
SELECT NEXT_DAY (SYSDATE, 'MONDAY') FROM DUAL;  -- Go to next Monday after today’s date (05-MAR-12)
SELECT LAST_DAY (SYSDATE) FROM DUAL;  -- Returns the last day of the month (29-FEB-12)
SELECT ROUND (SYSDATE, 'MONTH') FROM DUAL; --01-MAR-12
SELECT TRUNC (SYSDATE, 'MONTH') FROM DUAL; --01-FEB-12
SELECT ROUND (SYSDATE, 'YEAR') FROM DUAL;  --01-JAN-12
SELECT TRUNC (SYSDATE, 'YEAR') FROM DUAL;  --01-JAN-12
SELECT ROUND (SYSDATE, 'DAY') FROM DUAL;   --26-FEB-12
SELECT TRUNC (SYSDATE, 'DAY') FROM DUAL;   --26-FEB-12

EXTRACT Function:

An EXTRACT datetime function extracts and returns the value of a specified datetime field from a datetime or interval value expression. When you extract a TIMEZONE_REGION or TIMEZONE_ABBR (abbreviation), the value returned is a string containing the appropriate time zone name or abbreviation

The syntax of EXTRACT function is

EXTRACT ( YEAR / MONTH / WEEK / DAY / HOUR / MINUTE / TIMEZONE  FROM DATE)

Example:

SELECT EXTRACT(YEAR FROM SYSDATE) FROM DUAL; --Returns 2012
SELECT EXTRACT(MONTH FROM SYSDATE) FROM DUAL; --Returns 2
SELECT EXTRACT(DAY FROM SYSDATE) FROM DUAL; --Returns 27
SELECT EXTRACT(HOUR FROM SYSTIMESTAMP) FROM DUAL; --Returns 11
SELECT EXTRACT(MINUTE FROM SYSTIMESTAMP) FROM DUAL; --Returns 34

Have  a nice Day!

Max number in a Varchar column!


Well, to find the maximum number in a VARCHAR2 Column is bit tricky and we can find it in many ways. An example can be to find the maximum number in the Segment1 column in mtl_system_items_b table. Here is one of the best ways to find it:

select max(to_number(segment1))
FROM mtl_system_items_b
where regexp_like(segment1, '^-?[[:digit:],.]*$');

Solve your SUDOKU by SQL!


Oracle Database 11g Release 2 introduces a new feature called Recursive Subquery Factoring with the help of which you can solve your Sudoku.

Say you have a Sudoku like:

To solve this Sudoku you first have to transform this to a single string by appending all rows together:(give exact amount of spaces)

“53  7    6  195    98    6 8   6   34  8 3  17   2   6 6    28    419  5    8  79”

Past this string into a Recursive Subquery, run it and you get a new string with your solved Sudoku:


with x( s, ind ) as
( select sud, instr( sud, ' ' )
  from ( select '53 7 6 195 98 6 8 6 34 8 3 17 2 6 6 28 419 5 8 79' sud from dual )
  union all
  select substr( s, 1, ind - 1 ) || z || substr( s, ind + 1 )
  , instr( s, ' ', ind + 1 )
  from x
  , ( select to_char( rownum ) z
  from dual
  connect by rownum <= 9
       ) z
  where ind > 0
  and not exists ( select null
  from ( select rownum lp
                          from dual
  connect by rownum <= 9
                        )
  where z = substr( s, trunc( ( ind - 1 ) / 9 ) * 9 + lp, 1 )
  or z = substr( s, mod( ind - 1, 9 ) - 8 + lp * 9, 1 )
  or z = substr( s, mod( trunc( ( ind - 1 ) / 3 ), 3 ) * 3
  + trunc( ( ind - 1 ) / 27 ) * 27 + lp
  + trunc( ( lp - 1 ) / 3 ) * 6
                                   , 1 )
                 )
)
select s
from x
where ind = 0
/

The output:

534678912672195348198342567859761423426853791713924856961537284287419635345286179

This string can be transformed back to a nice display of the solution.

Solved in 1 Sec!….

My personal note: Sudoku is meant for human minds and not to be solved by a program. Hence you should enjoy solving them with your own minds. However you can use this if you are frozen at some point , unable to proceed further and frustration is about to begin…:)

Have a nice day!

FAQ’s in SQL & PL/SQL


FAQ’s in SQL & PL/SQL

 

What is PL/SQL?

PL/SQL is a procedural language that has both interactive SQL and procedural programming language constructs such as iteration, conditional branching.

 

What are the components of a PL/SQL Block?

Declarative part

Executable part

Exception part

 

What are the datatypes a available in PL/SQL?

Some scalar data types such as NUMBER, VARCHAR2, DATE, CHAR, LONG, BOOLEAN. Some composite data types such as RECORD & TABLE.

 

What are % TYPE and % ROWTYPE? What are the advantages of using these over datatypes?

% TYPE provides the data type of a variable or a database column to that variable.

% ROWTYPE provides the record type that represents a entire row of a table or view or columns selected in the cursor.

The advantages are:

I. Need not know about variable’s data type

ii. If the database definition of a column in a table changes, the data type of a variable changes accordingly.

 

What is difference between % ROWTYPE and TYPE RECORD?

% ROWTYPE is to be used whenever query returns an entire row of a table or view. TYPE RECORD is to be used whenever query returns columns of different table or views and variables.

 

Explain the two types of Cursors?

There are two types of cursors, Implicit Cursor and Explicit Cursor.

PL/SQL uses Implicit Cursors for queries.

User defined cursors are called Explicit Cursors. They can be declared and used.

 

What are the cursor attributes used in PL/SQL?

% ISOPEN – Used to check whether a cursor is open or not.

% ROWCOUNT – Used to check the number of rows fetched/updated/deleted.

% FOUND – Used to check whether cursor has fetched any row. True if rows are fetched.

% NOT FOUND – Used to check whether cursor has fetched any row. True if no rows are fetched.

 

What is a cursor for loop?

Cursor for loop implicitly declares %ROWTYPE as loop index, opens a cursor, fetches rows of values from active set into fields in the record and closes when all the records have been processed.

 

What is the difference between implicit and explicit cursors?

An explicit cursor is declared opened and fetched from in the program block where as an implicit cursor is automatically generated for SQL statements that process a single row only.

 

What are the different types of joins available in Oracle?

Equi Join: When primary and foreign key relationship exists between the tables that are going to be joined.

Self Join: If comparison comes in a single table

Cartesian Join: When tables are joined without giving any join condition.

Inner Join: The resultant set includes all the rows that satisfy the join condition.

Outer Join: The resultant set includes the rows which doesn’t satisfy the join condition.  The outer join operator Plus sign (+) will be included in the join condition.

 

What are SQLCODE and SQLERRM and why are they important for PL/SQL developers?

SQLCODE returns the value of the error number for the last error encountered. The SQLERRM returns the actual error message for the last error encountered. They can be used in exception handling to report, or, store in an error log table, the error that occurred in the code. These are especially useful for the WHEN OTHERS exception.

 

What is an autonomous transaction?

An autonomous transaction is an independent transaction that is initiated by another transaction (the parent transaction). An autonomous transaction can modify data and commit or rollback independent of the state of the parent transaction.

 

What is the difference between View and Materialized view?

Materialized view will not be refreshed every time you query the view. So to have good performance when data is not changed so rapidly, we use Materialized views rather than normal views which always fetches data from tables every time you run a query on it.

 

What is dynamic SQL?

Dynamic SQL allows you to construct a query, a DELETE statement, a CREATE TABLE statement, or even a PL/SQL block as a string and then execute it at runtime.

 

Can you use COMMIT in a trigger?

Yes but by defining an autonomous transaction.

 

What is the difference between anonymous blocks and stored procedures?

Anonymous block is compiled only when called. Stored procedure is compiled and stored in database with the dependency information as well. Former is PL/SQL code directly called from an application. Latter is stored in database. Former has declare statement. Latter doesn’t.

 

What is a package spec and package body? Why the separation?

Spec declares public constructs. Body defines public constructs, additionally declares and defines Private constructs.

Separation helps make development easier. Dependency is simplified. You can modify body without invalidating dependent objects.

 

What is Correlated Subquery?

Correlated Subquery is a subquery that is evaluated once for each row processed by the parent statement. Parent statement can be Select, Update or Delete.

 

What is Sequence?

Sequences are used for generating sequence numbers without any overhead of locking. Drawback is that after generating a sequence number if the transaction is rolled back, then that sequence number is lost.

 

What is SQL Deadlock?

Deadlock is a unique situation in a multi user system that causes two or more users to wait indefinitely for a locked resource. First user needs a resource locked by the second user and the second user needs a resource locked by the first user. To avoid dead locks, avoid using exclusive table lock and if using, use it in the same sequence and use Commit frequently to release locks.

 

What is SQL*Loader?

SQL*Loader is a product for moving data in external files into tables in an Oracle database. To load data from external files into an Oracle database, two types of input must be provided to SQL*Loader: the data itself and the control file.

 

What is the use of CASCADE CONSTRAINTS?

When this clause is used with the DROP command, a parent table can be dropped even when a child table exists.


Explain forward declaration used in functions?

A forward declaration means that modules (procedures and functions) are declared in advance of their actual body definition. This declaration makes that module available to be called by other modules even before the program’s body is defined. A forward declaration consists simply of the module header, which is just the name of the module followed by the parameter list (and a RETURN clause in case the module is a function), no more no less.

Forward declarations are required in one specific situation: mutual recursion.

 

What are SQLCODE and SQLERRM and why are they important for PL/SQL developers?

SQLCODE returns the value of the error number for the last error encountered. The SQLERRM returns the actual error message for the last error encountered. They can be used in exception handling to report, or, store in an error log table, the error that occurred in the code. These are especially useful for the WHEN OTHERS exception.

 

What is the difference between Truncate and Delete Commands?

 

TRUNCATE is a DDL command whereas DELETE is a DML command. Hence DELETE operation can be rolled back, but TRUNCATE operation cannot be rolled back. WHERE clause can be used with DELETE and not with TRUNCATE.

 

What is the Purpose of HAVING Clause?

The HAVING clause is used in combination with the GROUP BY clause. It can be used in a SELECT statement to filter the records that a GROUP BY returns.

 

What is INLINE View in SQL?

The inline view is a construct in Oracle SQL where you can place a query in the SQL FROM, clause, just as if the query was a table name.

 

While creating a sequence, what does cache and nocache options mean?

With respect to a sequence, the cache option specifies how many sequence values will be stored in memory for faster access.

 

Does the view exist if the table is dropped from the database?

Yes, in Oracle, the view continues to exist even after one of the tables (that the view is based on) is dropped from the database. However, if you try to query the view after the table has been dropped, you will receive a message indicating that the view has errors.

 

What is an Index?

An index is a performance-tuning method of allowing faster retrieval of records. An index creates an entry for each value that appears in the indexed columns. By default, Oracle creates B-tree indexes.

 

What types of index data structures can you have?

An index helps to faster search values in tables. The three most commonly used index-types are:

  • B-Tree: builds a tree of possible values with a list of row IDs that have the leaf value. Needs a lot of space and is the default index type for most databases.
  • Bitmap: string of bits for each possible value of the column. Each bit string has one bit for each row. Needs only little space and is very fast. (However, domain of value cannot be large, e.g. SEX(m,f); degree(BS,MS,PHD)
  • Hash: A hashing algorithm is used to assign a set of characters to represent a text string such as a composite of keys or partial keys, and compresses the underlying data. Takes longer to build and is supported by relatively few databases.

 

What is the difference between a “where” clause and a “having” clause?

“Where” is a kind of restriction statement. You use where clause to restrict all the data from DB. Where clause is used before result retrieving. But Having clause is using after retrieving the data. Having clause is a kind of filtering command.

 

Can a view be updated/inserted/deleted? If Yes – under what conditions?

A View can be updated/deleted/inserted if it has only one base table if the view is based on columns from one or more tables then insert, update and delete is not possible.

 

What is tkprof and how is it used?

The tkprof tool is a tuning tool used to determine cpu and execution times for SQL statements. You use it by first setting timed_statistics to true in the initialization file and then turning on tracing for either the entire database via the sql_trace parameter or for the session using the ALTER SESSION command. Once the trace file is generated you run the tkprof tool against the trace file and then look at the output from the tkprof tool. This can also be used to generate explain plan output.

 

What is explain plan and how is it used?

The EXPLAIN PLAN command is a tool to tune SQL statements. To use it you must have an explain_table generated in the user you are running the explain plan for. This is created using the utlxplan.sql script. Once the explain plan table exists you run the explain plan command giving as its argument the SQL statement to be explained. The explain_plan table is then queried to see the execution plan of the statement. Explain plans can also be run using tkprof.

 

What are the Lock types?

Share Lock: It allows the other users for only reading not to insert or update or delete.

Exclusive Lock: Only one user can have the privileges of insert or update and delete of particular object, others can only read.

Update Lock: Multiple user can read, update delete .

 

What is Pragma EXECPTION_INIT? Explain the usage?


The PRAGMA EXECPTION_INIT tells the complier to associate an exception with an oracle error.
E.g. PRAGMA EXCEPTION_INIT (exception name, oracle error number)

 

What is Raise_application_error?

Raise_application_error is a procedure of package DBMS_STANDARD which allows to issue a user_defined error messages from stored sub-program or database trigger.

 

What are the modes for passing parameters to Oracle?

There are three modes for passing parameters to subprograms
IN – An In-parameter lets you pass values to the subprogram being called. In the subprogram it acts like a constant and cannot be assigned a value.
OUT – An out-parameter lets you return values to the caller of the subprogram. It acts like an initialized variable its value cannot be assigned to another variable or to itself.
INOUT – An in-out parameter lets you pass initial values to the subprogram being called and returns updated values to the caller.

 

What is the difference between Package, Procedure and Functions?

A package is a database objects that logically groups related PL/SQL types, objects, and Subprograms.

Procedure is a sub program written to perform a set of actions and can return multiple values.

Function is a subprogram written to perform certain computations and return a single value.
Unlike subprograms packages cannot be called, passed parameters or nested.

 

How do you make a Function and Procedure as a Private?

Functions and Procedures can be made private to a package by not mentioning their declaration in the package specification and by just mentioning them in the package body.

 

What is Commit, Rollback and Save point?

Commit – Makes changes to the current transaction permanent. It erases the savepoints and releases the transaction locks.

Savepoint –Savepoints allow to arbitrarily hold work at any point of time with option of later committing. They are used to divide transactions into smaller portions.

Rollback – This statement is used to undo work.

 

What is the difference between DDL, DML and DCL structures?

DDL statements are used for defining data. Ex: Create, Alter, Drop, Truncate, Rename.
DML statements are used for manipulating data. Ex: Insert, update, truncate.
DCL statements are used for to control the access of data. Ex; Grant, Revoke.
TCL statements are used for data saving. Ex; Commit, Rollback, Savepoint.

 

What is the difference between the snapshot and synonym?

A snapshot refers to read-only copies of a master table or tables located on a remote node. A snapshot can be queried, but not updated; only the master table can be updated. A snapshot is periodically refreshed to reflect changes made to the master table. In this sense, a snapshot is really a view with periodicity.

A synonym is an alias for table, view, sequence or program unit. They are of two types private and public.

 

What is the difference between data types char and varchar?

Char reserves the number of memory locations mentioned in the variable declarations, even though not used (it can store a maximum of 255 bytes). Where as Varchar does not reserve any memory locations when the variable is declared, it stores the values only after they are assigned (it can store a maximum of 32767 bytes).

 

Can one call DDL statements from PL/SQL?

One can call DDL statements like CREATE, DROP, TRUNCATE, etc. from PL/SQL by using the “EXECUTE IMMEDATE” statement.

 

Tell some new features in PL/SQL in 10g?

-Regular expression functions REGEXP_LIKE, REGEXP_INSTR, REGEXP_REPLACE, and   REGEXP_SUBSTR

-Compile time warnings

– Conditional compilation

– Improvement to native compilation

– BINARY_INTEGER made similar to PLS_INTEGER

– Implicit conversion between CLOB and NCLOB

– Improved Overloading

– New datatypes BINARY_FLOAT, BINARY_DOUBLE

– Global optimization enabled

– PLS_INTEGER range increased to 32bit

– DYNAMIC WRAP using DBMS_DDL

 

What is Overloading in PL/SQL?

Overloading is an oops concept (Object Oriented Programming). By using the same name we can write any number of Procedures or functions in a package but either number of parameters in the procedure/function must vary or parameter datatype must vary.

 

What is a mutating and constraining table?

“Mutating” means “changing”. A mutating table is a table that is currently being modified by an update, delete, or insert statement. When a trigger tries to reference a table that is in state of flux (being changed), it is considered “mutating” and raises an error since Oracle should not return data that has not yet reached its final state.

Another way this error can occur is if the trigger has statements to change the primary, foreign or unique key columns of the table off which it fires. If you must have triggers on tables that have referential constraints, the workaround is to enforce the referential integrity through triggers as well.

 

What is Nested Table?

A nested table is a table within a table. A nested table is a collection of rows, represented as a column within the main table. For each record within main table, the nested table may contain multiple rows.  In a sense, it’s a way of storing a one-to many relationship within one table.

 

What is Varying Array?

A varying array is a set of objects, each with the same data types. The size of the array is limited when it is created. (When the table is created with a varying array, the array is a nested table with a limited set of rows). Varying arrays also known as VARRAYS, allows storing repeated attributes in tables.

 

Give some most often used predefined exceptions?

a) NO_DATA_FOUND (Select Statement returns no rows)
b) TOO_MANY_ROWS (Single row Select statement returns more than 1 row)
c) INVALID_CURSOR (Illegal cursor operations occurred)
d) CURSOR_ALREADY_OPEN (If cursor is opened & we are trying to reopen it)
e) INVALID_NUMBER (Conversion of Character to number fails)
f) ZERO_DIVIDE
g) DUP_VAL_ON_INDEX (Attempted to insert a duplicate value)

 

Give some important Oracle supplied packages?

DBMS_SQL: It is used to write Procedures & Anonymous blocks that use Dynamic SQL.

DBMS_JOB: Using it, we can submit PL/SQL programs for execution, execute PL/SQL programs on a schedule, identify when programs should run, remove programs from the schedule & suspend programs from running.

DBMS_OUTPUT: This package outputs values & messages from any PL/SQL block.

UTL_FILE: With this package, you can read from & write to Operating system files

UTL_HTTP: This package allows to make HTTP Requests directly from the database.

 

What is Instead Of Trigger?

This trigger is used to perform DML operation directly on the underlying tables, because a view cannot be modified by normal DML Statements if it contains joins or Group Functions. These triggers are Only Row Level Triggers. The CHECK option for views is not enforced when DML to the view are performed by Instead of Trigger.

 

What is the Sequence of Firing Database Triggers?

a) Before Row Level Trigger
b) Before Statement Level Trigger
c) After Row Level Trigger
d) Statement Operation
e) After Statement Level Trigger

 

What is the Difference between PL/SQL Table & Nested Table?

PL/SQL Table: Index by Tables are not Stored in Database.
Nested Table: Nested Tables are Stored in Database as Database Columns.

 

What is the Difference between Nested Table & Varray?

Nested Table
a) This are Sparse

b) We can Delete its Individual Elements
c) It do not have an Upper Boundary
d) This are Stored in System Generated Table

Varray
a) This are Dense

b) We cannot Delete its Elements
c) This are Fixed Size & always need to specify the size
d) These are Stored in Tablespaces

 

What are the various SQL Statements?

a) Data Retrieval: Select
b) DML: Insert, Update, Delete
c) DDL: Create, Alter, Drop, Rename, Truncate
d) Transaction Control: Commit, Rollback, Savepoint
e) DCL: Grant, Revoke
f) Session Control: Alter Session, Set Role
g) System Control: Alter System
h) Embedded SQL Statements: Open, Close, Fetch & Execute.

What is Rowid?

It is a Hexadecimal Representation of a Row in a Table. Rowid can only be Changed if we ‘Enable Row Movement’ on a Partitioned Table. Rowid’s of Deleted Rows can be Reused if Transaction is Committed.

 

What is Partitioning?

It Enables Tables & Indexes or Index-Organized tables to be subdivided into smaller manageable Pieces & these each small Piece is called Partition.
They are of following Types:
a) Range Partitioning
b) Hash Partitioning
c) List Partitioning
d) Composite Range-Hash Partitioning

What is a Cluster?

A cluster provides an optional method of storing table data. A cluster is comprised of a group of tables that share the same data blocks, which are grouped together because they share common columns and are often used together. For example, the EMP and DEPT table share the DEPTNO column. When you cluster the EMP and DEPT, Oracle physically stores all rows for each department from both the EMP and DEPT tables in the same data blocks. You should not use Clusters for tables that are frequently accessed individually.

 

What is the Difference between Nested Subquery & Correlated Subquery?

Nested Subquery
a) Inner Query runs first and executes once, returning values which are to be used by the Main query or outer query

b) Outer query is driver by Inner Query

Correlated Subquery
a) A Correlated Subquery or Inner Query execute once for each candidate row considered by outer query

b) Inner Query is Driven by Outer Query

 

What is the Difference between Translate & Replace?

Translate function converts each character in String with specified one whereas Replace function replaces part of the string in continuity by another sub-string.

 

Normalization / De-Normalization


Normalization:

It is the process of efficiently organizing data in a database. There are two goals of the normalization process:

  • Eliminate redundant data (for example, storing the same data in more than one table).
  • Ensure data dependencies make sense (only storing related data in a table). Both of these are worthy goals as they reduce the amount of space a database consumes and ensure that data is logically stored.

Eliminate Repeating Groups – Make a separate table for each set of related attributes, and give each table a primary key.
Eliminate Redundant Data – If an attribute depends on only part of a multi-valued key, remove it to a separate table.
Eliminate Columns Not Dependent On Key – If attributes do not contribute to a description of the key, remove them to a separate table.
Isolate Independent Multiple Relationships – No table may contain two or more 1:n or n:m relationships that are not directly related.
Isolate Semantically Related Multiple Relationships – There may be practical constrains on information that justify separating logically related many-to-many relationships.

1st Normal Form (1NF):

Def: A table (relation) is in 1NF if

1. There are no duplicated rows in the table.
2. Each cell is single-valued (i.e., there are no repeating groups or arrays).
3. Entries in a column (attribute, field) are of the same kind.

Note:

  • The order of the rows and columns are immaterial(of no importance).
  • The requirement that there be no duplicated rows in the table means that the table has a key (although the key might be made up of more than one column—even, possibly, of all the columns).

2nd Normal Form (2NF):

Def: A table is in 2NF if it is in 1NF and if all non-key attributes are dependent on all of the key.

Note: Since a partial dependency occurs when a non-key attribute is dependent on only a part of the (composite) key, the definition of 2NF is sometimes phrased as, “A table is in 2NF if it is in 1NF and if it has no partial dependencies.”

3rd Normal Form (3NF):

Def: A table is in 3NF if it is in 2NF and if it has no transitive dependencies.

Note: A transitive dependency is a type of functional dependency in which the value in a non-key field is determined by the value in another non-key field and that field is not a candidate key.

Boyce-Codd Normal Form (BCNF):

Def: A table is in BCNF if it is in 3NF and if every determinant is a candidate key.

4th Normal Form (4NF):

Def: A table is in 4NF if it is in BCNF and if it has no multi-valued dependencies. A multi-valued dependency occurs when, for each value in field A, there is a set of values for field B and a set of values for field C but fields B and C are not related.

5th Normal Form (5NF):

Def: A table is in 5NF, also called “Projection-Join Normal Form” (PJNF), if it is in 4NF and if every join dependency in the table is a consequence of the candidate keys of the table.

Domain-Key Normal Form (DKNF):

Def: A table is in DKNF if every constraint on the table is a logical consequence of the definition of keys and domains.

De-Normalization:

Denormalization is a technique to move from higher to lower normal forms of database modeling in order to speed up database access. You may apply Denormalization in the process of deriving a physical data model from a logical form.

Invoking SQL*Loader


Invoking SQL*Loader

On Unix systems, the command used to invoke SQL*Loader is sqlldr. On Windows systems running Oracle8i, release 8.1 or higher, the command is also sqlldr.

The command to execute SQL*Loader is as follows:

sqlldr USERID = <username>/<password> CONTROL = <control file name> LOG = <log file name>….

Issuing the sqlldr command by itself results in a list of valid command-line parameters being displayed. Command-line parameters are usually keyword/value pairs, and may be any combination of the following:

USERID = {username[/password] [@net_service_name]|/} Specifies the username and password to use when connecting to the database.

CONTROL = control_ file_name  Specifies the name, which may include the path, of the control file. The default extension is .ctl.

LOG = path_ file_name Specifies the name of the log file to generate for a load session. You may include a path as well. By default, the log file takes on the name of the control file, but with a .log extension, and is written to the same directory as the control file.

BAD = path_ file_name Specifies the name of the bad file. You may include a path as part of the name. By default, the bad file takes the name of the control file, but with a .bad extension, and is written to the same directory as the control file.

DATA = path_ file_name Specifies the name of the file containing the data to load. You may include a path as part of the name. By default, the name of the control file is used, but with the .dat extension.

DISCARD = path_ file_name Specifies the name of the discard file. You may include a path as part of the name. By default, the discard file takes the name of the control file, but it has a .dis extension.

Other Parameters are:

DISCARDMAX=logical_record_count

SKIP=logical_record_count

SKIP_INDEX_MAINTENANCE={TRUE | FALSE}

SKIP_UNUSABLE_INDEXES={TRUE | FALSE}

LOAD=logical_record_count

ERRORS=insert_error_count

ROWS=rows_in_bind_array

BINDSIZE=bytes_in_bind_array

SILENT=[(]keyword[,keyword...][)]

DIRECT={TRUE | FALSE}

PARFILE=path_file_name

PARALLEL={TRUE | FALSE}

READSIZE=bytes_in_read_buffer

FILE=database_datafile_name

My Previous Posts:

The Oracle DUAL table


The Oracle DUAL table

The DUAL Dummy table (as it is sometimes called) is an automatically-generated table assigned to SYS, but accessible to all users. It has a single column “DUMMY” of type VARCHAR2(1) which has a single row with a value of ‘X’.

SELECT * FROM DUAL;
D

X

DESC DUAL;
Name                        Null?                Type
—————————————————————————-
DUMMY                                             VARCHAR2(1)

What is it used for?

It is useful because it always exists, and has a single row, which is handy for select statements with constant expressions. You could just as easily do this with any other table with a single row, but using DUAL makes it portable among all Oracle installations.

SELECT 1+1 FROM DUAL;

SELECT SYSDATE  FROM DUAL;

SELECT USER FROM DUAL;

Why is it called “DUAL”?

The DUAL table was created by Chuck Weiss of Oracle corporation to provide a table for joining in internal views:

“I created the DUAL table as an underlying object in the Oracle Data Dictionary. It was never meant to be seen itself, but instead used inside a view that was expected to be queried. The idea was that you could do a JOIN to the DUAL table and create two rows in the result for every one row in your table. Then, by using GROUP BY, the resulting join could be summarized to show the amount of storage for the DATA extent and for the INDEX extent(s). The name, DUAL, seemed apt for the process of creating a pair of rows from just one.” Chuck Weiss, Oracle

The original DUAL table had two rows in it (hence its name), but subsequently it only had one row.

Note: Although it is possible to delete the one record, or insert additional records, one really should not do that!.

Few Interesting SQL Queries


Few Interesting SQL Queries

Here I have listed few interesting and useful SQL queries. Have fun! If you know more, you can share also.

1] Check Database / instance & machine you are using.

SQL> select name from v$database;

SQL> select instance_name from v$instance;

SQL> select * from global_name; 

2] Retrieve a random number using sql statement.

SQL> select dbms_random.random from dual;

3] Copy a table from one instance to another instance.

SQL> copy from apps/apps@vip replace xxtest1 or create xxtest1 using select * from xxtest1;

4] Check if your oracle applications instance is setup for Multi-Org ? 

SQL> select multi_org_flag from fnd_product_groups;

5] Check what patches have been already loaded.

SQL> select * from AD_APPLIED_PATCHES;

6] Check the database name.

SQL> select value from v$system_parameter where name = ‘db_name’;

7] Check the data Dictionary (includes all views and tables of the database).

SQL> select * from dictionary;

8] Check the definition data from a specific table (in this case, all tables with string “XXX”)

SQL> select * from ALL_ALL_TABLES where upper(table_name) like ‘%XXX%’;

9] Check the tables from actual user.

SQL> select * from user_tables;

10] Check all the objects of the connected user.

SQL> select * from user_catalog;

11] Check the Oracle products installed and version number.

SQL> select * from product_component_version;

12] Check the roles and roles privileges.

SQL> select * from role_sys_privs;

13] Check the integrity rules.

SQL> select constraint_name, column_name from sys.all_cons_columns;

14] Check all the tablespaces.

SQL> select * from V$TABLESPACE;

15] Oracle SQL query to know the database size.

SQL> select sum(BYTES)/1024/1024 MB from DBA_EXTENTS;

Sequence in Oracle


Sequence in Oracle

What is a Sequence?

  • A sequence is a user created database object that can be shared by multiple users to generate unique integers.
  • A typical usage for sequences is to create a primary key value, which must be unique for each row.
  • The sequence is generated and incremented (or decremented) by an internal Oracle routine.
  • This can be a time-saving object because it can reduce the amount of application code needed to write a sequence-generating routine.
  • Sequence numbers are stored and generated independently of tables. Therefore, the same sequence can be used for multiple tables.

You create a sequence using the CREATE SEQUENCE statement, which has the following syntax:

CREATE SEQUENCE sequence_name
[START WITH start_num]
[INCREMENT BY increment_num]
[ { MAXVALUE maximum_num | NOMAXVALUE } ]
[ { MINVALUE minimum_num | NOMINVALUE } ]
[ { CYCLE | NOCYCLE } ]
[ { CACHE cache_num | NOCACHE } ]
[ { ORDER | NOORDER } ];

 where

  1. The default start_num is 1.
  2. The default increment number is 1.
  3. The absolute value of increment_num must be less than the difference between maximum_num and minimum_num.
  4. minimum_num must be less than or equal to start_num, and minimum_num must be less than maximum_num.
  5. NOMINVALUE specifies the maximum is 1 for an ascending sequence or -10^26 for a descending sequence.
  6. NOMINVALUE is the default.
  7. maximum_num must be greater than or equal to start_num, and maximum_num must be greater than minimum_num.
  8. NOMAXVALUE specifies the maximum is 10^27 for an ascending sequence or C1 for a descending sequence.
  9. NOMAXVALUE is the default.
  10. CYCLE specifies the sequence generates integers even after reaching its maximum or minimum value.
  11. When an ascending sequence reaches its maximum value, the next value generated is the minimum.
  12. When a descending sequence reaches its minimum value, the next value generated is the maximum.
  13. NOCYCLE specifies the sequence cannot generate any more integers after reaching its maximum or minimum value.
  14. NOCYCLE is the default.
  15. CACHE cache_num specifies the number of integers to keep in memory.
  16. The default number of integers to cache is 20.
  17. The minimum number of integers that may be cached is 2.
  18. The maximum integers that may be cached is determined by the formula CEIL(maximum_num – minimum_num)/ABS(increment_num).
  19. NOCACHE specifies no integers are to be stored.
  20. ORDER guarantees the integers are generated in the order of the request.
  21. You typically use ORDER when using Real Application Clusters.
  22. NOORDER doesn’t guarantee the integers are generated in the order of the request.
  23. NOORDER is the default

Creating a sequence and then get the next value

CREATE SEQUENCE test_seq;

Sequence created.

SELECT test_seq.nextval FROM DUAL;

NEXTVAL
----------
    1

INSERT INTO test VALUES (test_seq.nextval,'Record A');                    
---Using a sequence to populate a table's column

Once initialized, you can get the current value from the sequence using currval.

SELECT test_seq.nextval FROM dual;

NEXTVAL
----------
     1
SELECT test_seq.currval FROM dual;

CURRVAL
----------
     1

You can’t use CURRVAL just after a sequence creation. It will throw an error.

create sequence deptno_seq start with 50 increment by 10;

Sequence created.

select deptno_seq.currval from dual;

select deptno_seq.currval
       *
ERROR at line 1:
ORA-08002: sequence DEPTNO_SEQ.CURRVAL is not yet defined in this session

select deptno_seq.currval, deptno_seq.nextval from dual;

CURRVAL    NEXTVAL
---------- ----------
     50         50               
----Will Work

When you select currval , nextval remains unchanged; nextval only changes when you select nextval to get the next value.

SELECT test_seq.nextval FROM dual;

NEXTVAL
----------
     1
SELECT test_seq.nextval, test_seq.currval FROM dual;

NEXTVAL    CURRVAL
---------   ---------
     2          2

Getting Information on Sequences

You get information on your sequences from user_sequences.

desc user_sequences;

 Name                    Null?             Type
 -------------------------------------------------------------------
 SEQUENCE_NAME     NOT NULL               VARCHAR2(30)
 MIN_VALUE                                NUMBER
 MAX_VALUE                                NUMBER
 INCREMENT_BY        NOT NULL            NUMBER
 CYCLE_FLAG                               VARCHAR2(1)
 ORDER_FLAG                               VARCHAR2(1)
 CACHE_SIZE           NOT NULL              NUMBER
 LAST_NUMBER         NOT NULL             NUMBER

select * from user_sequences;

Modifying a Sequence

  • You modify a sequence using the ALTER SEQUENCE statement.
  • You cannot change the start value of a sequence.
  • The minimum value cannot be more than the current value of the sequence ( currval ).
  • The maximum value cannot be less than the current value of the sequence ( currval ).

Removing a Sequence

• Remove a sequence from the data dictionary by using the DROP SEQUENCE statement.

• Once removed, the sequence can no longer be referenced.

DROP SEQUENCE dept_deptid_seq;

Sequence dropped.