MySQL选择左连接为空的行

您可以使用以下查询：

SELECt  table1.id FROM    table1         LEFT JOIN table2  ON table1.id IN (table2.user_one, table2.user_two)WHERe   table2.user_one IS NULL;

虽然，根据您的索引，

table2

SELECt  table1.id FROM    table1         LEFT JOIN table2 AS t1 ON table1.id = t1.user_one        LEFT JOIN table2 AS t2 ON table1.id = t2.user_twoWHERe   t1.user_one IS NULLAND     t2.user_two IS NULL;