MySQL 多选，多 Where 子句
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MySQL Multiple Select, Multiple Where Clauses
提问by user1114864
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.
我不想为一项操作运行数百个 SELECT 查询，而是只想运行一个大查询，我希望这会减轻我服务器上的负载。
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'))
)
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:
此查询中将有更多 SELECTS，但即使这两个也不起作用。当我运行此代码时，出现错误：
Operand should contain 1 column(s).
Any suggestions? Thanks!
有什么建议？谢谢！
回答by shola
You can try below may be but you may need UNION
您可以尝试以下可能但您可能需要 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')
回答by Explosion Pills
This is caused by the parentheses outside of the columns. Even something as simple as:
这是由列外的括号引起的。甚至像这样简单的事情：
SELECT ((SELECT 1), (SELECT 1))
Will yield this error -- the problem is that MySQL can only display one column per ... well ... column, and the entire ()wraps a single column. If you remove the outer parentheses it will display each SELECTin a separate column.
会产生这个错误——问题是 MySQL 只能显示每一列......好吧......列，并且整个()包装单列。如果删除外括号，它将SELECT在单独的列中显示每个括号。
