PL SQL

PL/SQL

Simply SQL mean – Structural Query Language ; PL is an extension to Sql, for making it as Programming Language Sql. PL/SQL combines the data-manipulating power of SQL with the processing power of procedural languages.

Variables

NAME is same as name and Name. The size of an identifier cannot exceed 30 characters. Identifiers should be descriptive. When possible, avoid obscure names such as cpm. Instead, use meaningful names such as cost_per_thousand.

  • %ROWTYPE and %TYPE – special data structures are provided by Oracle;
  • %TYPE has two advantages. First, you need not know the exact datatype of the table columns. Second, if you change the database definition of columns, such as employee_id or last_name. The data types of empid and emplname in Example: Using %TYPE With Table Columns change accordingly at run time.

Assignment operator (:=), a colon followed by an equal to sign.

Examples:

country := 'France'; -- single quotes !!
country := UPPER('Canada');
valid_id := TRUE; -- boolean
done := (counter > 100); -- boolean
deviation := -9.5e-3;

Boolean Values- can be one of TRUE, FALSE, and NULL.

Usage:

active_employee BOOLEAN NOT NULL := TRUE; -- value cannot be NULL
monthly_salary NUMBER(6) NOT NULL := 2000; -- value cannot be NULL

Datetime literals have various formats depending on the datetime data types like ‘4-Mar-2012 10:26 AM’ or ‘4-Mar-2012’

PL/Sql body structure

Declare
-- here define variables require + at the end of each var a semicolon(;)
Begin
NULL; -- NULL statement does nothing, allows this block to executed and tested
End; -- semicolon(;)

Note: Inside body “select” can be used and “into” is used to fill up defined variables. An anonymous block always expects a select statement with ‘into’ – keyword.

If you are using older version of sql-developer to display on the screen before body structure add SET SERVEROUTPUT ON.

DBMS_OUTPUT.PUT_LINE( 'The answer is: ' || answer ); -- command to test display in sql-developer

Usage of “UPDATE” and “SET”

UPDATE employees SET salary = salary + bonus WHERE employee_id = emp_id;
FOR i in 1..10 LOOP
DBMS_OUTPUT.PUT_LINE(' Hello world(1)');
END LOOP;
WHILE sal <= 15000 LOOP
DBMS_OUTPUT.PUT_LINE('Hello world(2) ')
END LOOP;
LOOP
counter := counter + 1; -- increment counter variable
total := total + counter * counter; -- compute total
-- exit loop when condition is true
EXIT WHEN total > 25000; -- LOOP until condition is met
END LOOP;
EXCEPTION
WHEN NO_DATA_FOUND THEN
INSERT INTO temp VALUES (NULL, NULL, 'Not found'); -- insert NULLs
COMMIT;
END;
--

While loop format

WHILE <> LOOP
.......................
END LOOP;

Goto

BEGIN
...............
GOTO print_now;
............
<>
.............
END;

Functions/Methods/Procedures

Cursor — this is like a pointer to table, points to only one row at a time
Function — function like add/Sub/ ,… SO..ON  ;  Like we send parameters and we get a return;
Procedure — use this when a lot of things to do …. and finally need to return one single value; generally select statement – proc for finding a person’s name with his id ;

UDD – user defined datatypes

Collections

collection types enable you to declare high-level data types similar to arrays, sets, and hash tables found in other languages.

DECLARE
-- declaring variables
TYPE jobids_array IS VARRAY(12) OF VARCHAR2(10); -- declare VARRAY
jobids jobids_array; -- declare a variable
BEGIN
jobids := jobids_array('AC_ACCOUNT', 'AC_MGR', 'AD_ASST', 'AD_PRES', 'AD_VP', 
 'FI_ACCOUNT', 'FI_MGR', 'HR_REP', 'IT_PROG', 'SH_CLERK',
 'ST_CLERK', 'ST_MAN');
END LOOP;
END;

How about now accessing our newly defined array?

variable_name=jobids(3);

Records

Records are composite data structures whose fields can have different data types. You can use records/collections to hold related items and pass them to sub-programs with a single parameter. When declaring records, you use the TYPE definition.

Declaration:

TYPE meeting_record
IS RECORD (
date_held DATE,
duration timerec, -- nested record
location VARCHAR2(20),
purpose VARCHAR2(50)
);

Usage:

meeting_record.location = Delhi;
FOR someone IN (SELECT * FROM employees WHERE employee_id < 120 )
LOOP
DBMS_OUTPUT.PUT_LINE('First name = ' || someone.first_name || ', Last name = ' || someone.last_name);
END LOOP;
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