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MySQL 8.4 參考手冊  /  ...  /  選擇特定欄位

5.3.4.3 選取特定欄位

如果您不想看到資料表的整個列,只需指定您感興趣的欄位,並用逗號分隔。例如,如果您想知道您的動物何時出生,請選擇 namebirth 欄位

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 |
+----------+------------+

若要找出誰擁有寵物,請使用此查詢

mysql> SELECT owner FROM pet;
+--------+
| owner  |
+--------+
| Harold |
| Gwen   |
| Harold |
| Benny  |
| Diane  |
| Gwen   |
| Gwen   |
| Benny  |
| Diane  |
+--------+

請注意,查詢僅從每筆記錄擷取 owner 欄位,其中某些欄位會重複出現。若要最小化輸出,請加入關鍵字 DISTINCT,以僅擷取每個唯一的輸出記錄一次

mysql> SELECT DISTINCT owner FROM pet;
+--------+
| owner  |
+--------+
| Benny  |
| Diane  |
| Gwen   |
| Harold |
+--------+

您可以使用 WHERE 子句將列選取與欄位選取結合。例如,若要僅取得狗和貓的出生日期,請使用此查詢

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 |
+--------+---------+------------+