Question

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MySQL – How to get a list of values in Table A that don’t exist in Table B?

I have three tables .

Table x:

+------+
| ID   |
+------+
|    1 |
|    2 |
|    3 |
|    4 |
+------+

Table Y

+------+
| ID   |
+------+
|    1 |
|    2 |
|    3 |
|    4 |
|    5 |
+------+

Table Z

+------+
| ID   |
+------+
|    1 |
|    2 |
|    3 |
|    4 |
|    5 |
|    6 |
|    7 |
+------+

I have to find the value exists in TABLE Z but it not exists in table X and Y .

Output:

+----+
| ID |
------
| 6  |
| 7  |
+----+

How can I get this?

Answer 1

You could use EXISTS to make a subquery.

SELECT tz.id 
FROM Z tz 
WHERE 
    NOT EXISTS (select 1 from X tx where tx.id = tz.id)
    AND NOT EXISTS (select 1 from Y ty where ty.id = tz.id)

@RaphaëlAlthaus’s answer is probably better on efficiency, though. See Can I get better performance using a JOIN or using EXISTS?

The MySQL reference has a section on EXISTS: 13.2.9.6. Subqueries with EXISTS or NOT EXISTS.