如果表 B 中的行不存在，如何从表 A 和表 B 中删除行

Question

I have 2 tables and I need to delete rows from both tables if A.itemID does not exist in table B
I've tried doing:
DELETE a,b FROM A a, B b WHERE NOT EXISTS (SELECT * FROM B b WHERE b.cid= a.itemID );
But I cant get the error: Error Code: 1093. You can't specify target table 'b' for update in FROM clause

All help is appreciated!

I have the following tables:

Table A 
+--------+--------+-------------+
|catId   | itemID | lastModified|
+--------+--------+-------------+
| 167262 | 678909 | 2017-10-01  |
| 167262 | 986785 | 2012-01-03  |
| 143210 | 456776 | 2018-04-30  |
| 143210 | 345676 | 2019-06-14  |
| 143210 | 010836 | 2016-03-09  |
| 379588 | 883567 | 2019-03-04  |
+--------+--------+-------------+
Table B 
+--------+----------+-------+
| cid    |locationid| Type  |
+--------+----------+-------+
| 678909 | 1        | a     |
| 986785 | 1        | a     |
| 143210 | 2        | b     |
| 883567 | 3        | a     |
+--------+----------+-------+ ```


My resulting tables would be :

Table A 
+--------+--------+-------------+
|catId   | itemID | lastModified|
+--------+--------+-------------+
| 167262 | 678909 | 2017-10-01  |
| 167262 | 986785 | 2012-01-03  |
| 379588 | 883567 | 2019-03-04  |

Table B
+--------+----------+-------+
| cid    |locationid| Type  |
+--------+----------+-------+
| 678909 | 1        | a     |
| 986785 | 1        | a     |
| 883567 | 3        | a     |
+--------+----------+-------+ 

Answer 1

I need to delete rows from both tables if A.itemID does not exist in table B

If the itemId does not match, then there is no row in B . So, you just need to delete in A . So:

DELETE a FROM a
    WHERE NOT EXISTS (SELECT 1
                      FROM B b
                      WHERE b.cid = a.itemID
                     );

Answer 2

You could also express your logic using a delete anti-join:

DELETE a
FROM A a
LEFT JOIN B b ON b.cid = a.itemID
WHERE b.cid IS NULL;

Answer 3

To add to Gordon Linoff's answer (which helped me get to my solution) the following shows how to view the records that will be deleted before doing it:

To view the records that WILL be affected:

SELECT TableA.ColumnName FROM TableA
WHERE NOT EXISTS 
(SELECT 1 FROM TableB WHERE TableB.ColumnName = TableA.ColumnName);

To then delete the affected rows:

DELETE TableA FROM TableA
WHERE NOT EXISTS 
(SELECT 1 FROM TableB WHERE TableB.ColumnName = TableA.ColumnName);

So, the only differences are change SELECT for DELETE and removing the ColumnName from after the SELECT word.