mysql查询仅在满足特定条件时才将条件应用于where子句

Question

我想通过测试condition_1将condition_2添加到mysql where子句中。condition_1是type = 'group:1'，condition_2是username = 'rahim'。所以，如果满足type = 'group:1'，那么我将在where子句中添加username = 'rahim'。如果不满意，我不想在where条款中添加这一点。我试过username = 'rahim' CASE WHEN type = 'group:1'。但是，它输出错误：

[Err]1064：在'CASE WHEN类型附近使用正确的语法="group:1"AND type='group:1">

 SELECT
    a.user_id,
    b.username,
    a.message,
    a.type
FROM
    livechat_message a
LEFT JOIN livechat_user b ON a.user_id = b.user_id
WHERE
    username = 'rahim' CASE
WHEN type = 'group:1'
AND type = 'group:1'

提前谢谢。

Answer 1

您似乎想要：

WHERE NOT (type = 'group:1' AND username <> 'rahim')