MySQL查询嵌套查询 [英] MySQL query nested query

问题描述

我正在尝试在 MySQL (phpmyadmin) 和通过 PHP 上运行嵌套查询，两者都导致相同的输出，但不正确.

I`m trying to run a nested query on MySQL (phpmyadmin) and via PHP, and both result in the same output which is incorrect.

注意:由于项目的敏感性，表名已被剪掉

NOTE: Table name have been clipped due to sensitivity of project

SELECT * FROM `table1` WHERE ID="SELECT `field1` FROM `table2` WHERE ID=1"

这将返回零行，尽管每个查询单独给出如下有效输出

This returns zero rows, although each query alone gives a valid output as below

SELECT `field1` FROM `table2` WHERE ID=1

给出所需的输出，当在主查询的第一部分中使用时，这个输出也提供了所需的内容.请帮忙.

Gives the required output, and this output when used in the first part of the main query provides also what is required. Please help.

推荐答案

不要用引号将其括起来.而是将其括在括号中:

Don't enclose it in quotes. Instead enclose it in parentheses:

SELECT * FROM `table1` WHERE ID=(SELECT `field1` FROM `table2` WHERE ID=1)

如果子查询需要多行，请使用 WHERE ID IN (SELECT...) 而不是 WHERE ID=(SELECT...)

If multiple rows are expected from the subquery, use WHERE ID IN (SELECT...) instead of WHERE ID=(SELECT...)

不过，使用 JOIN 可能会获得更好的性能:

You'll probably get better performance with a JOIN though:

SELECT table1.* 
FROM
  table1 JOIN table2 ON table1.ID = table2.field1
WHERE table1.ID = 1

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