帮忙写个sql语句

Question

sql

Answer 1

select a.id,a.name,b.need1,b.need2 from a,b where a.id=b.id

Answer 2

不行啊亲。
mysql> select * from a;
+------+------+
| id   | name |
+------+------+
| 1    | a    |
| 2    | b    |
| 3    | c    |
+------+------+
3 rows in set (0.00 sec)mysql> select * from b;
+------+------+-------+
| id   | need | need2 |
+------+------+-------+
| 3    | 1    | 2     |
+------+------+-------+
1 row in set (0.00 sec)mysql> select a.id,a.name,b.need,b.need2 from a,b where a.id=b.id;
+------+------+------+-------+
| id   | name | need | need2 |
+------+------+------+-------+
| 3    | c    | 1    | 2     |
+------+------+------+-------+
1 row in set (0.01 sec)

Answer 3

不行啊亲。
mysql> select * from a;
+------+------+
| id   | name |
+------+------+
| 1    | a    |
| 2    | b    |
| 3    | c    |
+------+------+
3 rows in set (0.00 sec)mysql> select * from b;
+------+------+-------+
| id   | need | need2 |
+------+------+-------+
| 3    | 1    | 2     |
+------+------+-------+
1 row in set (0.00 sec)mysql> select a.id,a.name,b.need,b.need2 from a,b where a.id=b.id;
+------+------+------+-------+
| id   | name | need | need2 |
+------+------+------+-------+
| 3    | c    | 1    | 2     |
+------+------+------+-------+
1 row in set (0.01 sec)左链接查询
 select a.id,a.name,b.need,b.need2 from a left join b on a.id=b.id;