3.3.4.3.選擇特殊列
3.3.4.3. 選擇特殊列
如果你不想看到表中的所有行,就命名你感興趣的列,用逗號分開。例如,如果你想要知道你的動物什么時候出生的,選擇name和birth列:
mysql> SELECT name, birth FROM pet;
+----------+------------+
| name | birth |
+----------+------------+
| Fluffy | 1993-02-04 |
| Claws | 1994-03-17 |
| Buffy | 1989-05-13 |
| Fang | 1990-08-27 |
| Bowser | 1989-08-31 |
| Chirpy | 1998-09-11 |
| Whistler | 1997-12-09 |
| Slim | 1996-04-29 |
| Puffball | 1999-03-30 |
+----------+------------+
找出誰擁有寵物,使用這個查詢:
mysql> SELECT owner FROM pet;
+--------+
| owner |
+--------+
| Harold |
| Gwen |
| Harold |
| Benny |
| Diane |
| Gwen |
| Gwen |
| Benny |
| Diane |
+--------+
請注意該查詢只是簡單地檢索每個記錄的owner列,并且他們中的一些出現多次。為了使輸出減到最少,增加關鍵字DISTINCT檢索出每個唯一的輸出記錄:
mysql> SELECT DISTINCT owner FROM pet;
+--------+
| owner |
+--------+
| Benny |
| Diane |
| Gwen |
| Harold |
+--------+
可以使用一個WHERE子句結合行選擇與列選擇。例如,要想查詢狗和貓的出生日期,使用這個查詢:
mysql> SELECT name, species, birth FROM pet
-> WHERE species = 'dog' OR species = 'cat';
+--------+---------+------------+
| name | species | birth |
+--------+---------+------------+
| Fluffy | cat | 1993-02-04 |
| Claws | cat | 1994-03-17 |
| Buffy | dog | 1989-05-13 |
| Fang | dog | 1990-08-27 |
| Bowser | dog | 1989-08-31 |
+--------+---------+------------+