My web site is a cafeteria. The user logs in and orders. When the same user logs in twice, the sub query error appears. What are the possible ways to solve the sub query problem?
1条回答 默认 最新
- duanfang7270 2017-06-18 06:48关注
If your subquery returns more than a single row, you can use an
IN
clause to manage more rows:select * from my_table where id in (select id from table2 where ....)
Or you can obtain a single result using an aggregation function:
select * from my_table where id = (select max(id) from table2 where ....)
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