MySQL-操作表记录：插入.更新.查询.删除

1. 表记录的插入
2. 表记录的更新
3. 表记录的查询
4. 表记录的删除

步骤一：创建stu_info表，并确保stu_info表记录为空。

在userdb库中创建stu_info表：

[root@zhangyx ~]# mysql -u root -p
Enter password:
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 5
Server version: 5.7.27-log MySQL Community Server (GPL)

Copyright (c) 2000, 2019, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> use userdb;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed

删除stu_info表的所有记录：

mysql> DELETE FROM stu_info;
Query OK, 0 rows affected (0.00 sec)        //stu_info表刚建立 删除零条记录
确认删除结果：
mysql> SELECT * FROM stu_info;
Empty set (0.00 sec)

步骤二：练习表记录的操作

1）插入记录时，指定记录的每一个字段的值

这种情况下，不需要明确指出字段，但每条记录的值的顺序、类型都必须与表格结构向一致，否则可能无法正确插入记录。
比如，以下操作将向stu_info表插入3条表记录：

mysql> INSERT stu_info VALUES
-> ('Jim','girl',24),
-> ('Tom','boy',21),
-> ('Lily','girl',20);
Query OK, 3 rows affected (0.15 sec)
Records: 3  Duplicates: 0  Warnings: 0

完成插入后确认表记录：

mysql> SELECT * FROM stu_info;
+------+--------+-----+
| name | gender | age |
+------+--------+-----+
| Jim  | girl   |  24 |
| Tom  | boy    |  21 |
| Lily | girl   |  20 |
+------+--------+-----+
3 rows in set (0.00 sec)

2）插入记录时，只指定记录的部分字段的值

这种情况下，必须指出各项值所对应的字段；而且，未赋值的字段应设置有默认值或者有自增填充属性或者允许为空，否则插入操作将会失败。
比如，向stu_info表插入Jerry的年龄信息，性别为默认的“boy”，自动编号，相关操作如下：

mysql> INSERT INTO stu_info(name,age)
-> VALUES('Jerry',27);
Query OK, 1 row affected (0.04 sec)

类似的，再插入用户Mike的年龄信息：

mysql> INSERT INTO stu_info(name,age)
-> VALUES('Mike',21);
Query OK, 1 row affected (0.05 sec)

确认目前stu_info表的所有记录：

mysql> SELECT * FROM stu_info;
+-------+--------+-----+
| name  | gender | age |
+-------+--------+-----+
| Jim   | girl   |  24 |
| Tom   | boy    |  21 |
| Lily  | girl   |  20 |
| Jerry | boy    |  27 |
| Mike  | boy    |  21 |
+-------+--------+-----+
5 rows in set (0.00 sec)

3）更新表记录时，若未限制条件，则适用于所有记录

将stu_info表中所有记录的age设置为10：

mysql> UPDATE stu_info SET age=10;
Query OK, 5 rows affected (0.04 sec)
Rows matched: 5  Changed: 5  Warnings: 0

确认更新结果：

mysql> SELECT * FROM stu_info;
+-------+--------+-----+
| name  | gender | age |
+-------+--------+-----+
| Jim   | girl   |  10 |
| Tom   | boy    |  10 |
| Lily  | girl   |  10 |
| Jerry | boy    |  10 |
| Mike  | boy    |  10 |
+-------+--------+-----+
5 rows in set (0.00 sec)

4）更新表记录时，可以限制条件，只对符合条件的记录有效

将stu_info表中所有性别为“boy”的记录的age设置为20：

mysql> UPDATE stu_info SET age=20
-> WHERE gender='boy';
Query OK, 3 rows affected (0.04 sec)
Rows matched: 3  Changed: 3  Warnings: 0

确认更新结果：

mysql> SELECT * FROM stu_info;
+-------+--------+-----+
| name  | gender | age |
+-------+--------+-----+
| Jim   | girl   |  10 |
| Tom   | boy    |  20 |
| Lily  | girl   |  10 |
| Jerry | boy    |  20 |
| Mike  | boy    |  20 |
+-------+--------+-----+
5 rows in set (0.00 sec)

5）删除表记录时，可以限制条件，只删除符合条件的记录

删除stu_info表中年龄小于18的记录：

mysql> DELETE FROM stu_info WHERE age < 18;
Query OK, 2 rows affected (0.03 sec)

确认删除结果：

mysql> SELECT * FROM stu_info;
+-------+--------+-----+
| name  | gender | age |
+-------+--------+-----+
| Tom   | boy    |  20 |
| Jerry | boy    |  20 |
| Mike  | boy    |  20 |
+-------+--------+-----+
3 rows in set (0.00 sec)

6）删除表记录时，如果未限制条件，则会删除所有的表记录

删除stu_info表的所有记录：

mysql> DELETE FROM stu_info;
Query OK, 3 rows affected (0.00 sec)

确认删除结果：

mysql> SELECT * FROM stu_info;
Empty set (0.00 sec)