SQL LEFT JOIN 与另一列的 where 子句

Posted 2023-02-24

【中文标题】SQL LEFT JOIN 与另一列的 where 子句

【英文标题】：SQL LEFT JOIN with where clause from another column

【发布时间】：2018-05-10 08:14:41

【问题描述】：

我正在尝试连接两列，其中条件基于右表中的 Delete 和 Active 列。

查询->

SELECT
    `s`.`slider_id` as `id`,
    `s`.`slider_type` as `type`,
    `s`.`slider_name` as `name`,
    `sd`.`slider_data_type` AS `sd_type`,
    `sd`.`slider_data_value` AS `sd_value`,
    `sd`.`slider_data_group` AS `sd_group`,
    `sd`.`slider_data_id` AS `sd_id`
FROM `sliders` AS `s`
LEFT OUTER JOIN `slider_data` AS `sd`
    ON `s`.`slider_id` = `sd`.`slider_data_s_id`
WHERE
    `s`.`slider_id` = '11' AND
    ( ( `sd`.`slider_data_active` = 1 AND `sd`.`slider_data_delete` =0 ) OR
      ( `sd`.`slider_data_active` IS NULL AND `sd`.`slider_data_delete` IS NULL ) )

当另一个或 RIGHT 表中没有符合条件的记录时，查询工作正常。但不是当

`sd`.`slider_data_active` = 0 AND `sd`.`slider_data_delete` = 1

当右表中的活动列和删除列为 0 和 1 时，我仍想从主表或左表中检索数据

活动 0 和删除 1 将等于右列中的 NULL

请问有什么解决方法吗？

【参考方案1】：

将WHERE 子句中的AND 条件移动到表连接条件（ON），当您在WHERE 子句中使用LEFT JOINED 表时，它的开始行为类似于INNER JOIN，并且仅在存在时给出结果找到完全匹配。

SELECT `s`.`slider_id` as `id`, `s`.`slider_type` as `type`, `s`.`slider_name` as `name`, `sd`.`slider_data_type` AS `sd_type`, `sd`.`slider_data_value` AS `sd_value`, `sd`.`slider_data_group` AS `sd_group`, `sd`.`slider_data_id` AS `sd_id` 
FROM `sliders` AS `s` 
LEFT OUTER JOIN `slider_data` AS `sd` ON `s`.`slider_id` = `sd`.`slider_data_s_id` AND ( ( `sd`.`slider_data_active` = 1 AND `sd`.`slider_data_delete` =0 ) OR ( `sd`.`slider_data_active` IS NULL AND `sd`.`slider_data_delete` IS NULL ) )
WHERE `s`.`slider_id` = '11'