compare two group data in sql

Question

I have a problem to compare two tables: A

id x
1  2
1  5
1  4
1  6 

B

id x
1  2
1  5
1  4
1  6 

I want to know if the data in table A and B are same with id=1.

Answer 1

This will list any rows with id=1 that are in a but aren't in b :

SELECT a.*
FROM a
LEFT JOIN b ON a.id = b.id AND a.x = b.x AND a.id = 1
WHERE b.x IS NULL;

In the left join, bx will be null when there's an {a.id, ax} pair that doesn't have a corresponding {b.id, bx} pair.

To list any rows with id=1 that are in b but not in a , just turn the query around:

SELECT b.*
FROM b
LEFT JOIN a ON b.id = a.id AND b.x = z.x AND b.id = 1
WHERE z.x IS NULL;

Combine the two to find which rows are in a but not b and are in b but not a . If the query returns no rows then the values in both tables for id=1 are identical. If it does return rows, they're the ones that are different.

SELECT a.*, b.*
FROM a
LEFT JOIN b ON a.id = b.id AND a.x = b.x AND a.id = 1
WHERE b.x IS NULL
UNION SELECT a.*, b.*
FROM b
LEFT JOIN a ON b.id = a.id AND b.x = z.x AND b.id = 1
WHERE z.x IS NULL;