Postgresql - ADD/ REMOVE - DEFAULT VALUE FROM A COLUMN

 -- EXAMPLE: MY_TABLE_NAME HAVE A DEFAULT TOTAL OF 0 

ALTER TABLE MY_TABLE_NAME ALTER COLUMN TOTAL_CENTS SET DEFAULT 0;

-- EXAMPLE: MY_TABLE_NAME ARE AVAILABLE BY DEFAULT

ALTER TABLE MY_TABLE_NAME ALTER COLUMN AVAILABLE SET DEFAULT TRUE;

ALTER TABLE MY_TABLE_NAME ALTER COLUMN TOTAL_CENTS DROP DEFAULT;

Postgresql - ADD NOT NULL & REMOVE NOT NULL CONSTRAINT

 ALTER TABLE MY_TABLE_NAME ALTER COLUMN EMAIL SET NOT NULL;

ALTER TABLE MY_TABLE_NAME ALTER COLUMN EMAIL DROP NOT NULL;

Postgresql - Add/Remove primary key

 ALTER TABLE MY_TABLE_NAME ADD PRIMARY KEY (COLUMN_1, COLUMN_2);

ALTER TABLE MY_TABLE_NAME DROP CONSTRAINT TEST1_PKEY;

Postgresql - Identify duplicate rows

SELECT (mytablename.*)::text, count(*)

FROM mytablename

GROUP BY mytablename.*

HAVING count(*) > 1

Postgresql - Copy data from one table to another

 INSERT INTO mytablenamenew SELECT * FROM mytablenameold;

Postgresql - Delete N number of rows

DELETE FROM mytablename

WHERE id IN (SELECT id FROM mytablename ORDER BY 1 LIMIT 30000)

Postgresql - Random number generation

update foo set bar = floor(random() * 9 + 1); 

SELECT random(),floor(random() * 9 + 1) LIMIT 10;

select floor(7000000000 + random() * 8999);