SELECT 中的 MySQL IF

Question

我有三个 MySQL InnoDB 表: 债务人 公司 个人

现在我想查找有关债务人的信息。 以下 SQL 不工作，任何人都可以帮助我编写工作 SQL 吗？

SELECT
    d.id,
    d.type,
    i.name
FROM
    debtors AS d
IF d.type = 'c' THEN
    INNER JOIN
        companies AS i ON (i.debtor_id = d.id)
ELSE THEN
    INNER JOIN
        private_individuals AS i ON (i.debtor_id = d.id)
WHERE
    d.id = 1

错误:

#1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'IF d.type = 'c' THEN INNER JOIN companies AS i ON (i.debtor_id = d.i' at line 7

提前致谢!

Answer 1

你不能那样使用 IF!

这是一个可能的解决方案:

SELECT
    d.id,
    d.type,
    COALESCE(i.name, i2.name) as name
FROM
    debtors AS d
    LEFT JOIN companies AS i ON i.debtor_id = d.id and d.type = 'c'
    LEFT JOIN private_individuals AS i2 ON i2.debtor_id = d.id and d.type <> 'c'
WHERE
    d.id = 1

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另一个可能是动态 SQL，但您应该避免使用它! :)