如果我下面的查询:
SELECT 1 FROM emp;
困惑在SELECT 1 FROM
我得到:
mysql> SELECT 1 FROM emp;
+---+
| 1 |
+---+
| 1 |
| 1 |
| 1 |
| 1 |
| 1 |
| 1 |
| 1 |
| 1 |
| 1 |
| 1 |
| 1 |
| 1 |
| 1 |
| 1 |
| 1 |
+---+
如果我做的:
SELECT 1 FROM emp e WHERE 20=e.deptno;
我得到:
mysql> SELECT 1 FROM emp e WHERE 20=e.deptno;
+---+
| 1 |
+---+
| 1 |
| 1 |
| 1 |
| 1 |
| 1 |
| 1 |
+---+
6 rows in set (0.00 sec)
如果我这样做:
mysql> SELECT deptno FROM emp;
+--------+
| deptno |
+--------+
| 10 |
| 10 |
| 10 |
| 20 |
| 20 |
| 20 |
| 20 |
| 20 |
| 20 |
| 30 |
| 30 |
| 30 |
| 30 |
| 30 |
| 100 |
+--------+
15 rows in set (0.00 sec)
我看到有6行与20
和6列在前面:SELECT 1 FROM emp e WHERE 20=e.deptno;
但如何在这些查询有关?
其实我不认为这个问题应该被关闭。是的,它显示了对SQL选择如何工作的知识缺乏,但它不太定位。 – 2013-04-22 10:50:15