MySQL多重选择，多重where子句

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问题描述

我不想只为一个操作运行数百个SELECT查询，而只是运行一个大查询，希望这可以减轻服务器的负载.

Instead of running hundreds of SELECT queries for one operation, I want to just run one big query, which I'm hoping will ease the load on my server.

SELECT (
(SELECT link_type_id FROM connections WHERE (node_to_id = '0' AND node_from_id = '1') OR (node_from_id = '1' AND node_to_id = '0')),
(SELECT link_type_id FROM connections WHERE (node_to_id = '0' AND node_from_id = '2') OR (node_from_id = '2' AND node_to_id = '0'))
)

此查询中将有更多的SELECTS，但即使这两个都不起作用.当我运行此代码时，出现错误:

There will be many more SELECTS in this query, but even the two aren't working. When I run this code I get the error:

Operand should contain 1 column(s).

有什么建议吗?谢谢！

推荐答案

您可以尝试以下操作，但可能需要UNION

You can try below may be but you may need UNION

SELECT link_type_id FROM connections
WHERE (node_to_id = '0' AND node_from_id = '1')
OR (node_from_id = '1' AND node_to_id = '0')
UNION
SELECT link_type_id FROM connections
WHERE (node_to_id = '0' AND node_from_id = '2')
OR (node_from_id = '2' AND node_to_id = '0')

这篇关于MySQL多重选择，多重where子句的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！