select 中的通配符

星號 * 可以用在 select 子句中表示所有的屬性。

mysql> select instructor.*
    -> from instructor, teaches
    -> where instructor.ID = teaches.ID;
+-------+------------+------------+----------+
| ID    | name       | dept_name  | salary   |
+-------+------------+------------+----------+
| 10101 | Srinivasan | Comp. Sci. | 65000.00
 
 |
| 10101 | Srinivasan | Comp. Sci. | 65000.00 |
| 10101 | Srinivasan | Comp. Sci. | 65000.00 |
| 12121 | Wu         | Finance    | 90000.00 |
| 15151 | Mozart     | Music      | 40000.00 |
| 22222 | Einstein   | Physics    | 95000.00 |
| 32343 | El Said    | History    | 60000.00 |
| 45565 | Katz       | Comp. Sci. | 75000.00 |
| 45565 | Katz       | Comp. Sci. | 75000.00
 
 |
| 76766 | Crick      | Biology    | 72000.00 |
| 76766 | Crick      | Biology    | 72000.00 |
| 83821 | Brandt     | Comp. Sci. | 92000.00 |
| 83821 | Brandt     | Comp. Sci. | 92000.00 |
| 83821 | Brandt     | Comp. Sci. | 92000.00 |
| 98345 | Kim        | Elec. Eng. | 80000.00 |
+-------+------------+------------+----------+
 

15 rows in set (0.01 sec)

它返回了 instructor 中所有的屬性。

元組的排序

SQL 為用戶提供了一些結果顯示的順序的控制，order by 子句可以讓查詢結果中元組按升序顯示，考慮按字典序列出 Physics 系的所有教師。

mysql> select name
    -> from instructor
    -> where dept_name = ‘Physics‘
    -> order by name;
+----------+
| name     |
+----------+
| Einstein |
| Gold     |
+----------+
2 rows in set (0.00 sec)

為了使用降序，我們可以用 desc 表示降序，完整地說，可以用 asc 表示升序，此外，排序可以在多個屬性上進行，例如我們希望按 salary 的降序列出整個 instructor 關系，如果有幾名教師工資相同，則按姓名升序排列。

mysql> select * 
    -> from instructor
    -> order by salary desc, name asc;
+-------+------------+------------+----------+
| ID    | name       | dept_name  | salary   |
+-------+------------+------------+----------+
| 22222 | Einstein   | Physics    | 95000.00 |
| 83821 | Brandt     | Comp. Sci. | 92000.00 |
| 12121 | Wu         | Finance    | 90000.00 |
| 33456 | Gold       | Physics    | 87000.00 |
| 98345 | Kim        | Elec. Eng. | 80000.00 |
| 76543 | Singh      | Finance    | 80000.00 |
| 45565 | Katz       | Comp. Sci. | 75000.00 |
| 76766 | Crick      | Biology    | 72000.00 |
| 10101 | Srinivasan | Comp. Sci. | 65000.00 |
| 58583 | Califieri  | History    | 62000.00 |
| 32343 | El Said    | History    | 60000.00 |
| 15151 | Mozart     | Music      | 40000.00 |
+-------+------------+------------+----------+
12 rows in set (0.00 sec)

where 子句謂詞

為了簡化 where 子句，SQL 提供 between 運算符來說明一個值落在一個閉區間內。
考慮查詢，找出工資在 90000 美元和 100000 美元之間的教師的姓名，直觀地有

mysql> select name 
    -> from instructor
    -> where salary <= 100000 and salary >= 90000;
+----------+
| name     |
+----------+
| Wu       |
| Einstein |
| Brandt   |
+----------+
3 rows in set (0.01 sec)

可以用 between 運算符改寫為

mysql> select name
    -> from instructor
    -> where salary between 90000 and 100000;
+----------+
| name     |
+----------+
| Wu       |
| Einstein |
| Brandt   |
+----------+
3 rows in set (0.01 sec)

類似的有 not between 運算符

mysql> select name
    -> from instructor
    -> where salary not between 90000 and 100000;
+------------+
| name       |
+------------+
| Srinivasan |
| Mozart     |
| El Said    |
| Gold       |
| Katz       |
| Califieri  |
| Singh      |
| Crick      |
| Kim        |
+------------+
9 rows in set (0.00 sec)

where 子句還支持在元組上進行比較，考慮查詢，查找 Biology 系講授了課程的所有教師的姓名和他們所講授的課程

mysql> select name, course_id
    -> from instructor, teaches
    -> where (instructor.ID, dept_name) = (teaches.ID, ‘Biology‘);
+-------+-----------+
| name  | course_id |
+-------+-----------+
| Crick | BIO-101   |
| Crick | BIO-301   |
+-------+-----------+
2 rows in set (0.00 sec)

基於 MySQL 的數據庫實踐（擴展運算）