douhan8581 2019-06-10 18:08
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使用多个where子句选择多个查询

I have two select queries I want to combine for faster performance. I'm a bit confused as I'm not sure if I could use a JOIN or LEFT JOIN or something else to make it faster.

Here are the two queries I want to combine:

Query 1:

SELECT id FROM users WHERE email = :email LIMIT 1

Then, if that row exists from query 1, then run query 2:

SELECT * FROM settings WHERE id = :id_from_query_1

thank you for any kind of help!

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  • dougehe2022 2019-06-10 18:17
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    When making a join query you can specify what column to join on. In this case it would be:

    select users.id, settings.*
    from users
    join settings on users.id = settings.id
    

    You could also use a double from clause which I think results in the same speed background wise that would look like:

    select users.id, settings.*
    from users, settings
    where users.id = settings.id
    

    If proper indexes are set a join should be faster than 2 selects. Ofcourse there are many factors when it comes to speed like load, network, what is cached and what isn't etc.

    本回答被题主选为最佳回答 , 对您是否有帮助呢?
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