摘要：表A,B,C select * from A as s1 left join B as s2 on s1.id = s2.id left join C as s3 on s2.x = s3.x where s1.xxx = '' 阅读全文

摘要：关于左连接、右连接和内连接 left，right，inner，full select * from A as s1 left join B as s2 on s1.id = s2.id 左连接：A表全显示，B表满足on的条件显示 右连接：B表全显示，A表满足on的条件显示 内连接：A，B表满足on的 阅读全文