AUTOCOMMIT in SQL- Simple and Useful

DML Statements or Data Manipulation Language statements will not be committed unless they are committed explicitly, But if you use any data definition language (DDL) statement before or after , then Oracle Database issues an implicit COMMIT.

There is a provision in Oracle to commit every DML Transaction automatically once its run. This is called AUTOCOMMIT. We can also turn AUTOCOMMIT on and off based on our requirement.

Below are commands to check for AUTOCOMMIT.

When AUTOCOMMIT IMMEDIATE is activated all the DML statements executed afterward will be treated as a transaction and will be committed to the Database.

We can also limit the number of AUTOCOMMIT to number that we want using the below command.

PROCEDURAL PARAMETER MODES IN PLSQL

There are three modes, which tells the compiler, how to treat the actual parameters, used during call.

1. They are IN, OUT AND IN OUT.

2.The default is IN PARAMETER (calls are by reference)

Take values from calling environment. Behaves like constant [during exec, sub-prog cant change value]

Actual parameter can be literals, expressions, or constants. Can be assigned default values.

3. OUT PARAMETER (calls are by value)

Must be specified, returns a value to calling environment.

Behaves like uninitialized variable.

a)Uninitialized variables hold nulls.b)During exec, sub-program shall change value.c)During exec, if not changed a null is returned to caller.

Actual parameter must be a variable. [Cannot be constant]

Cannot be assigned default values.

4. IN OUT PARAMETER (calls are by value.)

Must be specified,

a)Shall take values from caller / returns a value to caller.

Behaves like initialized variable.

a)Uninitialized variables hold nulls.b)During exec, sub-program shall change value.c)During exec, if not changed a old is returned to caller.d)Actual parameter must be a variable. [cannot be constant]

Actual parameter must be a variable. [cannot be constant]

Cannot be assigned default values.  

Note:To improve performance out and in out can be given a compiler hint no copy, requesting the compiler to pass by reference.

How to Create a Procedure with both IN and OUT Parameter

In this post I will try to explain how to create a procedure with both Input and output Parameter

Out parameter: The out parameter mode is used to return values to the caller of the subprogram.

In parameter: The in parameter mode is used to pass values to the subprogram.

First Let’s Create a table order_details

SQL> create table ORDER_DETAILS

2 (ordno varchar2(12),

3 itemcode varchar2(12),

4 qtyord number,

5 qtydeld number);

Table created.

SQL> INSERT INTO ORDER_DETAILS VALUES('1','ITEM4',300,300);

1 row created.

SQL> INSERT INTO ORDER_DETAILS VALUES('5','ITEM1',200,200);

1 row created.

SQL> INSERT INTO ORDER_DETAILS VALUES('7','ITEM1',300,200);

1 row created.

SQL> INSERT INTO ORDER_DETAILS VALUES('13','ITEM4', 20, 20);

1 row created.

SQL> INSERT INTO ORDER_DETAILS VALUES('31','ITEM2',300,300);

1 row created.

Below is the procedure which will pass the input parameter into the procedure as well as output the result into an initialized variable

SQL> ed

Wrote file afiedt.buf

1 create or replace procedure ORDERDETAILS(orno in varchar2,b in out varchar2

)

2 is

3 qtyor number;

4 qtydel number;

5 code varchar2(5);

6 begin

7 select QTYORD,QTYDELD,ITEMCODE into qtyor, qtydel, code from ORDER_DETAILS

where ORDNO=orno;

8 if qtydel < qtyor then

9 b:= code;

10 dbms_output.put_line('You supply less than what is ordered '||b);

11 elsif qtydel > qtyor then

12 b:= code;

13 dbms_output.put_line('You supply more than what is ordered '||b);

14 else

15 b:=code;

16 dbms_output.put_line('NOTHING WRONG WITH THE SUPPLY '||b);

17 end if;

18 exception

19 when no_data_found then

20 dbms_output.put_line('no data returned');

21 when TOO_MANY_ROWS then

22 dbms_output.put_line('MANY ITEMS WITH SAME ITEMCODE');

23 when OTHERS then

24 dbms_output.put_line('SOME OTHER ERROR');

25* end ORDERDETAILS;

26 /

Procedure created.

After successful compilation of the procedure we can execute the same by passing the parameters

Executing the Procedure with intialized variable:

SQL> set serveroutput on;

SQL> DECLARE

2 var varchar2(10):='123';

3 begin

4 ORDERDETAILS('23',var);

5 end;

6 /

no data returned

PL/SQL procedure successfully completed.

SQL> DECLARE

2 var varchar2(10):='232';

3 begin

4 ORDERDETAILS('7',var);

5 end;

6 /

You supply less than what is ordered ITEM1

PL/SQL procedure successfully completed.

Please let me know if you want to know how to execute the same procedure using initialized variables

A NOCOPY hints can be added to improve the performance (create or replace procedure ORDERDETAILS(orno in varchar2,b in out NOCOPY varchar2)

Using the NOCOPY hint tells the compiler to use pass by reference, so no temporary buffer is needed and no copy forward and copy back operations happen. Instead, any modification to the parameter values are written directly to the parameter variable .

Procedure To Check FOR ITEM LEVEL FROM THE ITEMS TABLE

Below I have tried to explain Creation of Items_table and Procedure to Find Items less in Quantity from the Items Table; 

SQL> CREATE TABLE ITEMS_TABLE(

2 ITEM_CODE VARCHAR2(12),

3 MINLEVL NUMBER(5),

4 QTYNOW NUMBER(5),

5 MAXLEVL NUMBER(5),

6 RATE NUMBER(9,2)

7 );

 TABLE CREATED.

SQL> INSERT INTO ITEMS_TABLE VALUES ('ITEM_01',100,80,175,120.99);

1 ROW CREATED.

SQL> INSERT INTO ITEMS_TABLE VALUES('ITEM_02',125,100,250,200.99);

1 ROW CREATED.

SQL> INSERT INTO ITEMS_TABLE VALUES('ITEM_03',100,200,325,200.99);

1 ROW CREATED.

SQL> INSERT INTO ITEMS_TABLE VALUES('ITEM_05',100,200,325,200.00);

1 ROW CREATED.

SQL> SELECT * FROM ITEMS_TABLE;

ITEM_CODE MINLEVL QTYNOW MAXLEVL RATE

------------ ---------- ---------- ---------- ----------

ITEM_01 100 80 175 120.99

ITEM_02 125 100 250 200.99

ITEM_03 100 200 325 200.99

ITEM_05 100 200 325 200

SQL> CREATE OR REPLACE PROCEDURE ITEMS_PROC(ITEM VARCHAR2)

2 IS

3 QTY_NOW NUMBER;

4 MIN_LEVEL NUMBER;

5 MAX_LEVEL NUMBER;

6 BEGIN

7 SELECT

8 QTYNOW,

9 MINLEVL,

10 MAXLEVL INTO QTY_NOW,MIN_LEVEL,MAX_LEVEL FROM

11 ITEMS_TABLE WHERE ITEM_CODE=ITEM;

12 IF QTY_NOW < MIN_LEVEL THEN

13 UPDATE ITEMS_TABLE SET QTYNOW=MINLEVL+QTYNOW WHERE ITEM_CODE=ITEM;

14 DBMS_OUTPUT.PUT_LINE('QTY UPDATED');

15 ELSE

16 DBMS_OUTPUT.PUT_LINE('ITEM PRESENT');

17 END IF;

18 EXCEPTION

19 WHEN NO_DATA_FOUND THEN

20 DBMS_OUTPUT.PUT_LINE('NO DATA RETURNED');

21 WHEN TOO_MANY_ROWS THEN

22 DBMS_OUTPUT.PUT_LINE('MANY ITEMS WITH SAME ITEM CODE');

23 WHEN OTHERS THEN

24 DBMS_OUTPUT.PUT_LINE('SOME OTHER ERROR');

25 END;

26 /

PROCEDURE CREATED.

SQL> EXEC ITEMS_PROC('ITEM_01');

PL/SQL PROCEDURE SUCCESSFULLY COMPLETED.

SQL> SELECT * FROM ITEMS_TABLE;

ITEM_CODE MINLEVL QTYNOW MAXLEVL RATE

------------ ---------- ---------- ---------- ----------

ITEM_01 100 180 175 120.99

ITEM_02 125 100 250 200.99

ITEM_03 100 200 325 200.99

ITEM_05 100 200 325 200

SQL> EXEC ITEMS_PROC('ITEM_03');

PL/SQL PROCEDURE SUCCESSFULLY COMPLETED.

SQL> SELECT * FROM ITEMS_TABLE;

ITEM_CODE MINLEVL QTYNOW MAXLEVL RATE

------------ ---------- ---------- ---------- ----------

ITEM_01 100 180 175 120.99

ITEM_02 125 100 250 200.99

ITEM_03 100 200 325 200.99

ITEM_05 100 200 325 200

Using Group by clause along with ROLLUP or CUBE operators

Use the ROLLUP OPERATOR to produce subtotal values, ROLLUP IS AN EXTENSION OF GROUP BY

CLAUSE, Use the CUBE OPERATOR to produce cross-tabulation values. Use the GROUPING function

to identify the row values created by ROLLUP or CUBE. These operators and GROUPING function

can best be used ALONG WITH GROUP FUNCTIONS, as group functions operate on a set of rows to

give one result per group.

Examples of Rollup:

SQL> select deptno,sum(sal) from emp where deptno <30 group by rollup(deptno);

DEPTNO SUM(SAL)

---------- ----------

10 8750

20 10875

19625

SQL> select deptno,job,sum(sal) from emp where deptno <30 group by rollup(deptno,job);

DEPTNO JOB SUM(SAL)

---------- --------- ----------

10 CLERK 1300

10 MANAGER 2450

10 PRESIDENT 5000

10 8750

20 CLERK 1900

20 ANALYST 6000

20 MANAGER 2975

20 10875

19625

Example of CUBE:

The cube operator is used to produce results sets that are typically used for cross-tabular reports.

This means Rollup produces only one possible subtotaling where as Cube produces subtotal for all

possible conditions of grouping specified in the group by clause and a grand total

SQL> select deptno,sum(sal) from emp where deptno <30 group by cube(deptno);

DEPTNO SUM(SAL)

---------- ----------

19625

10 8750

20 10875

The following query produces subtotaling results based on job,based on deptno and based on the

individual jobs(clerk or analyst or manager etc in dept 10 and 20)

SQL> select deptno,job,sum(sal) from emp where deptno <30

group by cube(deptno,job);

DEPTNO JOB SUM(SAL)

---------- --------- ----------

19625

CLERK 3200

ANALYST 6000

MANAGER 5425

PRESIDENT 5000

10 8750

10 CLERK 1300

10 MANAGER 2450

10 PRESIDENT 5000

20 10875

20 CLERK 1900

DEPTNO JOB SUM(SAL)

---------- --------- ----------

20 ANALYST 6000

20 MANAGER 2975

13 rows selected.

NVL2 Function In Oracle

The nvl2 (expr1, expr2, expr3) works as follows:

if expr1 is not null it returns expr2, If expr1 is null it returns expr3.

SQL> select ename,nvl2(comm,comm,0),comm from emp order by comm;ENAME NVL2(COMM,COMM,0) COMM---------- ----------------- ---------TURNER 0 0ALLEN 300 300WARD 500 500MARTIN 1400 1400SMITH 0JONES 0JAMES 0MILLER 0FORD 0ADAMS 0BLAKE 0CLARK 0SCOTT 0KING 014 rows selected.

SQL> select ename, vsize (ename) from emp;ENAME VSIZE(ENAME)---------- ------------SMITH 5ALLEN 5WARD 4JONES 5MARTIN 6BLAKE 5CLARK 5SCOTT 5KING 4TURNER 6ADAMS 5JAMES 5FORD 4MILLER 614 rows selected.

SQL> select ename,nvl2(comm,comm,null),comm from emp order by comm;ENAME NVL2(COMM,COMM,NULL) COMM---------- -------------------- ----------TURNER 0 0ALLEN 300 300WARD 500 500MARTIN 1400 1400SMITHJONESJAMESMILLERFORDADAMS

BLAKE

ENAME NVL2(COMM,COMM,NULL) COMM---------- -------------------- ----------CLARKSCOTTKING14 rows selected.

SQL> select ename,nvl2(comm,null,0),comm from emp order by comm;ENAME NVL2(COMM,NULL,0) COMM---------- ----------------- ----------TURNER 0ALLEN 300WARD 500MARTIN 1400SMITH 0JONES 0JAMES 0MILLER 0FORD 0ADAMS 0BLAKE 0

ENAME NVL2(COMM,NULL,0) COMM---------- ----------------- ----------CLARK 0SCOTT 0KING 014 rows selected.

What are Sub Queries in ORACLE

Nesting of queries, i.e., a query which is inside another query. Here the outer query is called the parent query, which gets a result from the inner query. So the inner query gets executed first and based on its result the outer query gets executed. Note1:

Do no add an order by clause to a sub query. Use single row operator with single row sub query. Use multiple row operators with multiple-row sub query. The single row sub query operators are =, >, <, <=, >=, <>, ^=, != The multiple row operators are IN, ANY, ALL

Note: 2

‘=any’ means IN and ‘!=all’ means NOT IN

Note: 3

<any means less than maximum >any means greater than minimum <all means less than minimum >all means greater than maximum

SUB-QUERIES:SINGLE ROW SUB QUERY

SQL> select * from emp where sal>(select sal from emp where ename='SCOTT');

EMPNO ENAME JOB HIREDATE SAL DEPTNO--------- ---------- --------- --------- --------- --- --------- 7839 KING PRESIDENT 17-NOV-81 5000 10

SQL >select * from emp where sal>=(select sal from emp where ename='SCOTT');

  EMPNO ENAME JOB HIREDATE SAL DEPTNO--------- ---------- --------- --------- --------- --------- 7788 SCOTT ANALYST 09-DEC-82 3000 20 7839 KING PRESIDENT 17-NOV-81 5000 10 7902 FORD ANALYST 03-DEC-81 3000 20

SQL >select ename,job from emp where job=(select job from emp where empno=7369);

ENAME JOB---------- ---------SMITH CLERKADAMS CLERKJAMES CLERKMILLER CLERK

SQL > select ename,job from emp where job=(select job from emp where empno=7369)and sal>(select sal from emp where empno=7876);

ENAME JOB---------- ---------MILLER CLERK

  SQL >select * from emp where job='CLERK';

EMPNO ENAME JOB HIREDATE SAL DEPTNO --------- - --------- --------- --------- --------- -------------------- 7369 SMITH CLERK 17-DEC-80 800 20 7876 ADAMS CLERK 12-JAN-83 1100 20 7900 JAMES CLERK 03-DEC-81 950 30 7934 MILLER CLERK 23-JAN-82 1300 10

SUB-QUERIES: MULTIPLE ROW SUB QUERY

SQL >select empno,ename,sal from emp where sal=any(select sal from emp,salgrade where emp.sal between salgrade.losal and salgrade.hisal);

EMPNO ENAME SAL--------- ---------- ---------

7369 SMITH 800 7900 JAMES 950 7876 ADAMS 1100 7521 WARD 1250 7654 MARTIN 1250 7934 MILLER 1300 7844 TURNER 1500 7499 ALLEN 1600 7782 CLARK 2450 7698 BLAKE 2850 7566 JONES 2975 7788 SCOTT 3000 7902 FORD 3000 7839 KING 500014 rows selected.

SQL >select empno,ename,sal from emp where sal !=all (select sal from emp,salgrade where emp.sal between salgrade.losal and salgrade.hisal);

no rows selected

Decode Function in Oracle

Decode helps us to use conditional inquires by doing the work of a case or if-then-else statement (switch or if-then-else). The syntax is:

Decode(col/expression,search1,result1 [,search2,result2] [,search3,result3] [,search4,result4] […………………..] [, default])

SQL> select ename, empno, sal, job,

decode (job,'MANAGER', sal+5000) new_sal from emp;

ENAME EMPNO SAL JOB NEW_SAL

---------- --------- --------- --------- ---------

SMITH 7369 800 CLERK

ALLEN 7499 1600 SALESMAN

WARD 7521 1250 SALESMAN

JONES 7566 2975 MANAGER 7975

MARTIN 7654 1250 SALESMAN

BLAKE 7698 2850 MANAGER 7850

CLARK 7782 2450 MANAGER 7450

SCOTT 7788 3000 ANALYST

KING 7839 5000 PRESIDENT

TURNER 7844 1500 SALESMAN

ADAMS 7876 1100 CLERK

JAMES 7900 950 CLERK

FORD 7902 3000 ANALYST

MILLER 7934 1300 CLERK

14 rows selected.

SQL> select ename, empno, sal,

decode (job,'MANAGER',SAL+5000) "N_S", job from emp;

ENAME EMPNO SAL N_S JOB

---------- --------- --------- --------- ---------

SMITH 7369 800 CLERK

ALLEN 7499 1600 SALESMAN

WARD 7521 1250 SALESMAN

JONES 7566 2975 7975 MANAGER

MARTIN 7654 1250 SALESMAN

BLAKE 7698 2850 7850 MANAGER

CLARK 7782 2450 7450 MANAGER

SCOTT 7788 3000 ANALYST

KING 7839 5000 PRESIDENT

TURNER 7844 1500 SALESMAN

ADAMS 7876 1100 CLERK

JAMES 7900 950 CLERK

FORD 7902 3000 ANALYST

MILLER 7934 1300 CLERK

14 rows selected.

SQL> select job, sal, decode (job,'ANALYST',sal*1.10, 'CLERK',SAL*1.15, 'MANAGER',sal*1.20,sal)

"rev_sal" from emp ORDER BY JOB;

JOB SAL rev_sal

--------- --------- ---------

ANALYST 3000 3300

ANALYST 3000 3300

CLERK 800 920

CLERK 1100 1265

CLERK 1300 1495

CLERK 950 1092.5

MANAGER 2975 3570

MANAGER 2450 2940

MANAGER 2850 3420

PRESIDENT 5000 5000

SALESMAN 1600 1600

SALESMAN 1250 1250

SALESMAN 1500 1500

SALESMAN 1250 1250

14 rows selected.

SQL> select ename,sal,deptno,decode(deptno,10,

decode(job,'MANAGER',sal+4000,sal),sal+1000) "new_sal" from emp;

ENAME SAL DEPTNO new_sal

---------- --------- --------- ---------

SMITH 800 20 1800

ALLEN 1600 30 2600

WARD 1250 30 2250

JONES 2975 20 3975

MARTIN 1250 30 2250

BLAKE 2850 30 3850

CLARK 2450 10 6450

SCOTT 3000 20 4000

KING 5000 10 5000

TURNER 1500 30 2500

ADAMS 1100 20 2100

JAMES 950 30 1950

FORD 3000 20 4000

MILLER 1300 10 1300

14 rows selected.

What are EXTERNAL TABLES in Oracle?

DEFINITION: You can user external table feature to access external files as if they are tables inside the database.

When you create an external table, you define its structure and location with in oracle.

When you query the table, oracle reads the external table and returns the results just as if the data had been stored with in the database.

ACCESSING EXTERNAL TABLE DATA

To access external files from within oracle, you must first use the create directory command to define a directory object pointing to the external file location

Users who will access the external files must have the read and write privilege on the directory.

Ex:

CREATING DIRECTORY AND OS LEVEL FILE

   SQL> Sqlplus system/manager

   SQL> Create directory saketh_dir as ‘/Visdb/visdb/9.2.0/external’;

   SQL> Grant all on directory saketh_dir to saketh;

   SQL> Conn saketh/saketh

   SQL> Spool dept.lst

   SQL> Select deptno || ‘,’ || dname || ‘,’ || loc from dept;

   SQL> Spool off

CREATING EXTERNAL TABLE

 SQL> Create table dept_ext

         (deptno number(2),

         Dname varchar(14),

         Loc varchar(13))

         Organization external  ( type oracle_loader

                                                 Default directory saketh_dir

                                                 Access parameters

                                                 ( records delimited by newline

                                                    Fields terminated by “,”

                                                    ( deptno number(2),

                                                      Dname varchar(14),

                                                      Loc varchar(13)))

         Location (‘/Visdb/visdb/9.2.0/dept.lst’));

SELECTING DATA FROM EXTERNAL TABLE

SQL> select * from dept_ext;

This will read from dept.lst which is a operating system level file.

LIMITATIONS ON EXTERNAL TABLES

a)   You can not perform insert, update, and delete operations

b)   Indexing not possible

c)   Constraints not possible

BENEFITS OF EXTERNAL TABLES

a)  Queries of external tables complete very quickly even though a full table scan id required with each access

b)   You can join external tables to each other or to standard tables