82 lines
1.5 KiB
Markdown
82 lines
1.5 KiB
Markdown
查询数据
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=========================
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使用 `SELECT` 语句查询表中的内容。
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示例如下：
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假设有如下所示数据的表 `a`。
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```sql
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obclient> CREATE TABLE a (id int, name varchar(50), num int);
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Query OK, 0 rows affected (0.07 sec)
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obclient> INSERT INTO a VALUES(1,'a',100),(2,'b',200),(3,'a',50);
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Query OK, 3 rows affected (0.00 sec)
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Records: 3 Duplicates: 0 Warnings: 0
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obclient> SELECT * FROM a;
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+------+------+------+
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| ID | NAME | NUM |
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+------+------+------+
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| 1 | a | 100 |
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| 2 | b | 200 |
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| 3 | a | 50 |
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+------+------+------+
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3 rows in set (0.00 sec)
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```
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1. 从表 `a` 中读取 `name` 的数据。
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```sql
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obclient> SELECT name FROM a;
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+------+
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| NAME |
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+------+
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| a |
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| b |
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| a |
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+------+
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3 rows in set (0.00 sec)
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```
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2. 在查询结果中对 `name` 进行去重处理。
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```sql
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obclient> SELECT DISTINCT name FROM a;
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+------+
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| NAME |
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+------+
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| a |
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| b |
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+------+
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2 rows in set (0.01 sec)
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```
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3. 从表 `a` 中根据筛选条件 `name = 'a'` ，输出对应的 `id` 、`name` 和 `num`。
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```sql
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obclient> SELECT id, name, num FROM a WHERE name = 'a';
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+------+------+------+
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| ID | NAME | NUM |
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+------+------+------+
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| 1 | a | 100 |
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| 3 | a | 50 |
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+------+------+------+
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2 rows in set (0.00 sec)
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```
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更多 `SELECT` 语句相关的语法说明请参见《SQL 参考（MySQL 模式）》中 [SELECT](../../10.sql-reference/5.sql-statement/54.SELECT.md)章节。
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