Question

我对此查询有点问题。它运作得很好，但我是DRY的粉丝，这看起来很容易改进：

SELECT
    users.*,
    (
        SELECT user_information.value
        FROM users
        LEFT JOIN user_information
        ON user_information.userid = users.id
        WHERE user_information.name = 'account_name'
    ),
    (
        SELECT user_information.value
        FROM users
        LEFT JOIN user_information
        ON user_information.userid = users.id
        WHERE user_information.name = 'account_code'
    ),
    (
        SELECT user_information.value
        FROM users
        LEFT JOIN user_information
        ON user_information.userid = users.id
        WHERE user_information.name = 'account_id'
    ),
WHERE ...

部分：

SELECT user_information.value
FROM users
LEFT JOIN user_information
ON user_information.userid = users.id

每个子查询中完全相同（将来会有大约10个子查询），但where子句每次都会更改。是否可以将其保存在变量中，然后在mysql中附加每个where子句时使用它？

Answer 1

您可以将user_information表加入查询并对结果进行分组：

SELECT   users.*,
         GROUP_CONCAT(IF(i.name = 'account_name', i.value, NULL)),
         GROUP_CONCAT(IF(i.name = 'account_code', i.value, NULL)),
         GROUP_CONCAT(IF(i.name = 'account_id'  , i.value, NULL))
FROM     users LEFT JOIN user_information AS i ON i.userid = users.id
WHERE    ...
GROUP BY users.id

将查询保存在变量中然后添加where子句？

1 个答案: