Select Common Column Values in SQL

Question

I have a SQL table like

 docid            State
12                  MP
13                  MP
14                  MP
13                  CG
14                  CG
12                  MH
13                  MH
16                  DL

I want a SQL query where I can get a result with only common "docid" for all the three states "MP","CG","MH"

Like

Docid   
13

Note: States are entered from user id in Where states = ""

Answer 1

I just used sqlite3 to reproduce your scenario using the following SQL commands:

CREATE TABLE tablename (
    docid INT,
    State VARCHAR(2)
);
INSERT INTO tablename VALUES (12,'MP');
INSERT INTO tablename VALUES (13,'MP');
INSERT INTO tablename VALUES (14,'MP');
INSERT INTO tablename VALUES (13,'CG');
INSERT INTO tablename VALUES (14,'CG');
INSERT INTO tablename VALUES (12,'MH');
INSERT INTO tablename VALUES (13,'MH');
INSERT INTO tablename VALUES (16,'DL');

Then I was able to query what you are looking for using:

SELECT mp.docid AS Docid
FROM tablename AS mp
JOIN tablename AS cg ON mp.docid = cg.docid
JOIN tablename AS mh ON cg.docid = mh.docid
WHERE mp.State='MP' AND cg.State='CG' AND mh.State='MH';

which returned 13