How To Create Sequence In PostgreSQL And Usage Of Sequence || Table Prim...

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How To Create Sequence In PostgreSQL And Usage Of Sequence || Table Primary Key || Stored Procedure

CREATE SEQUENCE tbl_emp_seq

START WITH 1 -- VALUE WILL START WITH 1

INCREMENT BY 1 -- IT WILL GET INCREMENT BY 1

MINVALUE 1 -- MINIMUM VALUE CAN BE 1

MAXVALUE 10 -- MAXIMUM VALUE CAN BE 10

CYCLE; -- CYCLE MEANS, AFTER REACHING MAXVALUE, WHICH IS 10 HERE, THE SEQUENCE WILL START AGAIN FROM 1

-- NOW LET'S SEE THE SEQUENCE VALUE

-- USE THE BELOW STATEMENT FOR SEQUENCE VALUE

SELECT NEXTVAL('tbl_emp_seq');

-- THE VALUE REACHED MAXVALUE, NOW IT WILL AGAIN START FROM 1

-- NOW LET'S SEE THE CASE OF NO CYCLE

-- IN CASE OF NO CYCLE, THE SEQUENCE WON'T START AGAIN FROM 1

-- IT WILL THROW AN ERROR AFTER REACHING THE MAX VALUE

DROP SEQUENCE tbl_emp_seq;

CREATE SEQUENCE tbl_emp_seq

START WITH 1 -- VALUE WILL START WITH 1

INCREMENT BY 1 -- IT WILL GET INCREMENT BY 1

MINVALUE 1 -- MINIMUM VALUE CAN BE 1

MAXVALUE 10 -- MAXIMUM VALUE CAN BE 10

NO CYCLE; 

SELECT NEXTVAL('tbl_emp_seq');

-- HERE THE MAX VALUE IS REACHED, SO IF WE TRY TO GET THE VALUE AFTER THAT, WE WILL GET AN ERROR

ERROR:  nextval: reached maximum value of sequence "tbl_emp_seq" (10)

SQL state: 2200H

-- THIS IS WHY WE USUALLY KEEP THE MAXVALUE VERY HIGH AS MUCH POSSIBLE

-- NOW LET'S CREATE AN ACTUAL SEQUENCE AND USE IN A TABLE TO GENERATE VALUES AUTOMATICALLY

CREATE SEQUENCE tbl_emp_seq

START WITH 1 -- VALUE WILL START WITH 1

INCREMENT BY 1 -- IT WILL GET INCREMENT BY 1

MINVALUE 1 -- MINIMUM VALUE CAN BE 1

MAXVALUE 10000000000 -- MAXIMUM VALUE CAN BE 10

NO CYCLE; 

CREATE TABLE EMP

(

EMP_ID INTEGER DEFAULT NEXTVAL('tbl_emp_seq'),

EMP_NAME VARCHAR(50),

SALARY NUMERIC(5,2)

);

INSERT INTO EMP(EMP_NAME,SALARY) VALUES ('AKRAM',100.56);

INSERT INTO EMP(EMP_NAME,SALARY) VALUES ('SOHAIL',670.56);

INSERT INTO EMP(EMP_NAME,SALARY) VALUES ('KNOWLEDGE 360',757.87);

SELECT * FROM EMP;

-- WE CAN SEE, THE EMP_ID VALUES ARE GENERATED FROM SEQUENCE

-- NOW LET'S USE THE SEQUENCE IN A STORED PROCEDURE

CREATE OR REPLACE PROCEDURE public.EMP_PROC()

LANGUAGE 'plpgsql'

AS $BODY$

DECLARE

V_EMP_SEQ_VAL INTEGER;

BEGIN

SELECT NEXTVAL('tbl_emp_seq') into V_EMP_SEQ_VAL;

insert into emp(emp_id,emp_name,salary) values (V_EMP_SEQ_VAL,'New Emp',455.24);

END;

$BODY$;

call public.EMP_PROC();

select * from emp;

SELECT NEXTVAL('tbl_emp_seq');

SELECT CURRVAL('tbl_emp_seq');

-- also we can see the current value of a sequence

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