我有两个表，如果表b中不存在a.itemid，我需要从两个表中删除行
我试过做：
从不存在的a，b中删除a，b（从b中选择*，其中b.cid=a.itemid）；
但我不能得到错误：错误代码：1093。不能在from子句中为update指定目标表“b”
感谢您的帮助！
我有以下表格：

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     |
+--------+----------+-------+