56,867
社区成员




mysql> set @i:=0;
Query OK, 0 rows affected (0.03 sec)
mysql> select a.*, (@i:=@i+1) as row_id
-> from
-> (
-> select a.*,b.id as bid
-> from
-> (select 1 as id union all select 2) a
-> left join( select 1 as id ) b on a.id=b.id
-> order by b.id
-> )a;
+----+------+--------+
| id | bid | row_id |
+----+------+--------+
| 2 | NULL | 1 |
| 1 | 1 | 2 |
+----+------+--------+
2 rows in set (0.03 sec)
第一个套层子查询封闭一下也是正确的,不知道为啥
这句话什么意思