Stored Procedures
What is a Stored Procedure?
A stored procedure or in simple a proc is a named PL/SQL block which performs one or more specific task. This is similar to a procedure in other programming languages. A procedure has a header and a body. The header consists of the name of the procedure and the parameters or variables passed to the procedure. The body consists or declaration section, execution section and exception section similar to a general PL/SQL Block. A procedure is similar to an anonymous PL/SQL Block but it is named for repeated usage.We can pass parameters to procedures in three ways.
1) IN-parameters
2) OUT-parameters
3) IN OUT-parameters
A procedure may or may not return any value.
General Syntax to create a procedure is:
CREATE [OR REPLACE] PROCEDURE proc_name [list of parameters]
IS
Declaration section
BEGIN
Execution section
EXCEPTION
Exception section
END;IS - marks the beginning of the body of the procedure and is similar to DECLARE in anonymous PL/SQL Blocks. The code between IS and BEGIN forms the Declaration section.
The syntax within the brackets [ ] indicate they are optional. By using CREATE OR REPLACE together the procedure is created if no other procedure with the same name exists or the existing procedure is replaced with the current code.
The below example creates a procedure ‘employer_details’ which gives the details of the employee.
1> CREATE OR REPLACE PROCEDURE employer_details
2> IS
3> CURSOR emp_cur IS
4> SELECT first_name, last_name, salary FROM emp_tbl;
5> emp_rec emp_cur%rowtype;
6> BEGIN
7> FOR emp_rec in sales_cur
8> LOOP
9> dbms_output.put_line(emp_cur.first_name || ' ' ||emp_cur.last_name
10> || ' ' ||emp_cur.salary);
11> END LOOP;
12>END;
13> /
How to execute a Stored Procedure?
There are two ways to execute a procedure.1) From the SQL prompt.
EXECUTE [or EXEC] procedure_name;2) Within another procedure – simply use the procedure name.
procedure_name;
PL/SQL Functions
What is a Function in PL/SQL?
A function is a named PL/SQL Block which is similar to a procedure. The major difference between a procedure and a function is, a function must always return a value, but a procedure may or may not return a value.The General Syntax to create a function is:
CREATE [OR REPLACE] FUNCTION function_name [parameters]
RETURN return_datatype;
IS
Declaration_section
BEGIN
Execution_section
Return return_variable;
EXCEPTION
exception section
Return return_variable;
END;1) Return Type: The header section defines the return type of the function. The return datatype can be any of the oracle datatype like varchar, number etc.
2) The execution and exception section both should return a value which is of the datatype defined in the header section.
For example, let’s create a frunction called ''employer_details_func' similar to the one created in stored proc
1> CREATE OR REPLACE FUNCTION employer_details_func
2> RETURN VARCHAR(20);
3> IS
5> emp_name VARCHAR(20);
6> BEGIN
7> SELECT first_name INTO emp_name
8> FROM emp_tbl WHERE empID = '100';
9> RETURN emp_name;
10> END;
11> /In the example we are retrieving the ‘first_name’ of employee with empID 100 to variable ‘emp_name’.
The return type of the function is VARCHAR which is declared in line no 2.
The function returns the 'emp_name' which is of type VARCHAR as the return value in line no 9.
How to execute a PL/SQL Function?
A function can be executed in the following ways.1) Since a function returns a value we can assign it to a variable.
employee_name := employer_details_func;If ‘employee_name’ is of datatype varchar we can store the name of the employee by assigning the return type of the function to it.
2) As a part of a SELECT statement
SELECT employer_details_func FROM dual;3) In a PL/SQL Statements like,
dbms_output.put_line(employer_details_func);
This line displays the value returned by the function.
