[英]MySql find out if record's id is in another table (in one query)
可以说我有2张桌子:
Table 1: (customers)
------------------------------------------
id | name | etc... | etc..
Table 2: (blockList)
------------------------
id
我想知道每个客户是否存在于blockList表中,因为我正在遍历客户表(在单个查询中,作为单独的字段)
像这样: SELECT * FROM customers, blockList ORDER BY id DESC
您需要使用join,例如:
SELECT c.*, b.id AS id_blocklist
FROM customers AS c
LEFT JOIN blocklist AS b ON b.id = c.id
ORDER BY c.id DESC
如果只希望记录在阻止列表中,请使用INNER JOIN
您必须指定表连接
SELECT * FROM customers as c, blockList as b WHERE c.id = b.id ORDER BY id DESC
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