联表查询重复字段加表前缀

$alias = 'car';
//$this->_repeating_field = ['user_id','business_code', 'employee_id'];
if (!$field) {
    $field = "*";
}
foreach ($param as $k => $li) {
    if (in_array($k, $this->_repeating_field)) {
        $where[$alias . '.' . $k] = $li;
    } elseif ($k) {
        $where[$k] = $li;
    }
}

update/delete  where in select 当in的数量过大给性能带来很大问题

联表更新

UPDATE items,month SET items.price='12' WHERE items.id=month.id;
UPDATE a LEFT JOIN b on a.id=b.a_id SET a.title='aaaaa',b.body='bbbb' WHERE a.id=1

注意：多表 UPDATE 不可以使用 ORDER BY 或 LIMIT。

联表删除

从数据表t1中把那些id值在数据表t2里有匹配的记录全删除掉

DELETE t1 FROM t1,t2 WHERE t1.id=t2.id 
//DELETE FROM t1 USING t1,t2 WHERE t1.id=t2.id

 从数据表t1里在数据表t2里没有匹配的记录查找出来并删除掉

DELETE t1 FROM t1 LEFT JOIN T2 ON t1.id=t2.id WHERE t2.id IS NULL 
//DELETE FROM t1,USING t1 LEFT JOIN T2 ON t1.id=t2.id WHERE t2.id IS NULL

 从两个表中找出相同记录的数据并把两个表中的数据都删除掉

DELETE t1,t2 from t1 LEFT JOIN t2 ON t1.id=t2.id WHERE t1.id=25

 注意此处的delete t1,t2 from 中的t1,t2不能是别名