Question

sql如何写四张表结构如下：A[id, 字段1], B[id,A_id, C_id], C[id], D[id, C_i

Answer 1

SELECT * FROM a LEFT JOIN b ON a.`id` = b.`A_id` WHERE a.`字段1`='值' AND b.`C_id` IN (SELECT d.`C_id` FROM d);