软件测试修炼之路 A Tester

MySQL-约束和数据表操作

2016-07-19
Dex

外键约束的要求解析

  1. 约束保证数据的完整性和一致性
  2. 约束分为表级约束和列级约束
  3. 约束类型包括:
    1. NOT NULL(非空约束)
    2. PRIMARY KEY(主键约束)
    3. UNIQUE KEY(唯一约束)
    4. DEFAULT(默认约束)
    5. FOREIGN KEY(外键约束)

FOREIGN KEY:

  • 保持数据一致性,完整性。
  • 实现一对一或一对多关系。

外键约束的要求

  1. 父表和子表必须使用相同的存储引擎,而且禁止使用临时表。
  2. 数据表的存储引擎只能为InnoDB。
  3. 外键列和参照列必须具有相似的数据类型。其中数字的长度或是否有符号位必须相同;而字符的长度则可以不同。
  4. 外键列和参照列必须创建索引。如果外键列不存在索引的话,MySQL将自动创建索引。

编辑数据表的默认存储引擎

修改MySQL配置文件:

default-storage-engine=INNODB

演示外键约束

创建数据表:

mysql> CREATE TABLE provinces(
    -> id SMALLINT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
    -> pname VARCHAR(20) NOT NULL
    -> );
Query OK, 0 rows affected (0.07 sec)

查看数据表DB类型:

mysql> SHOW CREATE TABLE provinces;
+-----------+---------------------------------------------------------------------------------------------------------------------------------------------------	------------------------+
| Table     | Create Table

                        |
+-----------+---------------------------------------------------------------------------------------------------------------------------------------------------	------------------------+
| provinces | CREATE TABLE `provinces` (
  `id` smallint(5) unsigned NOT NULL AUTO_INCREMENT,
  `pname` varchar(20) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-----------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.02 sec)

创建一个users表,建立外键约束:

mysql> CREATE TABLE users(
    -> id SMALLINT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
    -> username VARCHAR(10) NOT NULL,
    -> pid BIGINT,
    -> FOREIGN KEY(pid) REFERENCES provinces(id)
    -> );
ERROR 1215 (HY000): Cannot add foreign key constraint

出现错误,因为users表的pidprovinces表中的id字段的数据类型不一致。

创建users表,字段和provincesid字段数据类型一致,但默认是有符号位的:

mysql> CREATE TABLE users(
    -> id SMALLINT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
    -> username VARCHAR(10) NOT NULL,
    -> pid SMALLINT,
    -> FOREIGN KEY(pid) REFERENCES provinces(id)
    -> );
ERROR 1215 (HY000): Cannot add foreign key constraint

依然报错,所以符号位也必须要一致。

再次修改新建表的sql:

mysql> CREATE TABLE users(
    -> id SMALLINT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
    -> username VARCHAR(10) NOT NULL,
    -> pid SMALLINT UNSIGNED,
    -> FOREIGN KEY(pid) REFERENCES provinces(id)
    -> );
Query OK, 0 rows affected (0.11 sec)

创建users表成功。

这时,users表为子表,provinces为父表;user.pid为外键列,provinces.id为参照列。

查看参照列索引:

mysql> SHOW INDEXES FROM provinces\G;
*************************** 1. row ***************************
        Table: provinces
   Non_unique: 0
     Key_name: PRIMARY
 Seq_in_index: 1
  Column_name: id
    Collation: A
  Cardinality: 0
     Sub_part: NULL
       Packed: NULL
         Null:
   Index_type: BTREE
      Comment:
Index_comment:
1 row in set (0.00 sec)

ERROR:
No query specified

注:\G为查询结果按列打印。

查看外键列索引:

mysql> SHOW INDEXES FROM userS \G;
*************************** 1. row ***************************
        Table: users
   Non_unique: 0
     Key_name: PRIMARY
 Seq_in_index: 1
  Column_name: id
    Collation: A
  Cardinality: 0
     Sub_part: NULL
       Packed: NULL
         Null:
   Index_type: BTREE
      Comment:
Index_comment:
*************************** 2. row ***************************
        Table: users
   Non_unique: 1
     Key_name: pid
 Seq_in_index: 1
  Column_name: pid
    Collation: A
  Cardinality: 0
     Sub_part: NULL
       Packed: NULL
         Null: YES
   Index_type: BTREE
      Comment:
Index_comment:
2 rows in set (0.01 sec)

ERROR:
No query specified

查看users表的表结构:

mysql> SHOW CREATE TABLE users\G;
*************************** 1. row ***************************
       Table: users
Create Table: CREATE TABLE `users` (
  `id` smallint(5) unsigned NOT NULL AUTO_INCREMENT,
  `username` varchar(10) NOT NULL,
  `pid` smallint(5) unsigned DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `pid` (`pid`),
  CONSTRAINT `users_ibfk_1` FOREIGN KEY (`pid`) REFERENCES `provinces` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

ERROR:
No query specified

外键约束的参照操作

  1. CASCADE:从父表或更新且自动删除或更新子表中匹配的行
  2. SET NULL:从父表删除或更新行,并设置子表中的外键列为NULL。如果使用该选项,必须保证子表列没有指定NOT NULL。
  3. RESTRICT:拒绝对父表的删除或更新操作。
  4. NO ACTION:标准SQL的关键字,在MySQL中与RESTRICT相同。

创建一个新表:

mysql> CREATE TABLE users1(
    -> id SMALLINT UNSIGNED PRIMARY KEY AUTO_INCREMENT,
    -> username VARCHAR(10) NOT NULL,
    -> pid SMALLINT UNSIGNED,
    -> FOREIGN KEY(pid) REFERENCES provinces(id) ON DELETE CASCADE
    -> );
Query OK, 0 rows affected (0.11 sec)

查看表结构:

mysql> SHOW CREATE TABLE users1\G;
*************************** 1. row ***************************
       Table: users1
Create Table: CREATE TABLE `users1` (
  `id` smallint(5) unsigned NOT NULL AUTO_INCREMENT,
  `username` varchar(10) NOT NULL,
  `pid` smallint(5) unsigned DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `pid` (`pid`),
  CONSTRAINT `users1_ibfk_1` FOREIGN KEY (`pid`) REFERENCES `provinces` (`id`) ON DELETE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

ERROR:
No query specified

provinces表中插入几条数据:

mysql> INSERT provinces(pname) VALUES('A');
Query OK, 1 row affected (0.10 sec)

mysql> INSERT provinces(pname) VALUES('B');
Query OK, 1 row affected (0.01 sec)

mysql> INSERT provinces(pname) VALUES('C');
Query OK, 1 row affected (0.00 sec)

mysql> SELECT * FROM provinces;
+----+-------+
| id | pname |
+----+-------+
|  1 | A     |
|  2 | B     |
|  3 | C     |
+----+-------+
3 rows in set (0.03 sec)

在users1表插入记录:

mysql> INSERT users1(username,pid) VALUES('Tom',3);
Query OK, 1 row affected (0.02 sec)

mysql> INSERT users1(username,pid) VALUES('John',7);
ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint
ails (`test`.`users1`, CONSTRAINT `users1_ibfk_1` FOREIGN KEY (`pid`) REFERENCE
 `provinces` (`id`) ON DELETE CASCADE)

第二条记录出错,因为pid为7,在父表中不存在,所以出错。

继续插入两条数据:

mysql> INSERT users1(username,pid) VALUES('Rose',2);
Query OK, 1 row affected (0.00 sec)

mysql> INSERT users1(username,pid) VALUES('John',3);
Query OK, 1 row affected (0.00 sec)

mysql> SELECT * FROM users1;
+----+----------+------+
| id | username | pid  |
+----+----------+------+
|  1 | Tom      |    3 |
|  3 | Rose     |    2 |
|  4 | John     |    3 |
+----+----------+------+
3 rows in set (0.00 sec)

中间插入失败一次,id值也会递增1。

删除id为3的记录:

mysql> DELETE FROM provinces WHERE id=3;
Query OK, 1 row affected (0.07 sec)

查看父表和子表的结果:

mysql> SELECT * FROM provinces;
+----+-------+
| id | pname |
+----+-------+
|  1 | A     |
|  2 | B     |
+----+-------+
2 rows in set (0.00 sec)

mysql> SELECT * FROM users1;
+----+----------+------+
| id | username | pid  |
+----+----------+------+
|  3 | Rose     |    2 |
+----+----------+------+
1 row in set (0.00 sec)

表级约束与列级约束

  • 对一个数据列建立的约束,称为列级约束。
  • 对多个数据列简历的约束,称为标记约束。
  • 列级约束既可以在列定义时声明,也可以在列定义后声明。
  • 表级约束只能在列定义后声明。

修改数据表-添加/删除列

添加单列

语法:

ALTER TABLE tbl_name ADD [COLUMN] col_name column_definition [FIRST | AFTER col_name]

查看users1表结构:

mysql> SHOW COLUMNS FROM users1;
+----------+----------------------+------+-----+---------+----------------+
| Field    | Type                 | Null | Key | Default | Extra          |
+----------+----------------------+------+-----+---------+----------------+
| id       | smallint(5) unsigned | NO   | PRI | NULL    | auto_increment |
| username | varchar(10)          | NO   |     | NULL    |                |
| pid      | smallint(5) unsigned | YES  | MUL | NULL    |                |
+----------+----------------------+------+-----+---------+----------------+
3 rows in set (0.02 sec)

增加一列:

mysql> ALTER TABLE users1 ADD age TINYINT UNSIGNED NOT NULL DEFAULT 10;
Query OK, 0 rows affected (0.23 sec)
Records: 0  Duplicates: 0  Warnings: 0

再增加一列:

mysql> ALTER TABLE users1 ADD password1 VARCHAR(32) NOT NULL AFTER username;
Query OK, 0 rows affected (0.10 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> SHOW COLUMNS FROM users1;
+-----------+----------------------+------+-----+---------+----------------+
| Field     | Type                 | Null | Key | Default | Extra          |
+-----------+----------------------+------+-----+---------+----------------+
| id        | smallint(5) unsigned | NO   | PRI | NULL    | auto_increment |
| username  | varchar(10)          | NO   |     | NULL    |                |
| password1 | varchar(32)          | NO   |     | NULL    |                |
| pid       | smallint(5) unsigned | YES  | MUL | NULL    |                |
| age       | tinyint(3) unsigned  | NO   |     | 10      |                |
+-----------+----------------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)

再插入一列,并查看表结构:

mysql> ALTER TABLE users1 ADD truename VARCHAR(20) NOT NULL FIRST;
Query OK, 0 rows affected (0.10 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> SHOW COLUMNS FROM users1;
+-----------+----------------------+------+-----+---------+----------------+
| Field     | Type                 | Null | Key | Default | Extra          |
+-----------+----------------------+------+-----+---------+----------------+
| truename  | varchar(20)          | NO   |     | NULL    |                |
| id        | smallint(5) unsigned | NO   | PRI | NULL    | auto_increment |
| username  | varchar(10)          | NO   |     | NULL    |                |
| password1 | varchar(32)          | NO   |     | NULL    |                |
| pid       | smallint(5) unsigned | YES  | MUL | NULL    |                |
| age       | tinyint(3) unsigned  | NO   |     | 10      |                |
+-----------+----------------------+------+-----+---------+----------------+
6 rows in set (0.00 sec)

添加多列

语法:

ALTER TABLE tbl_name ADD [COLUMN] (col_name column_definition...)

删除列

ALTER TABLE tbl_name DROP col_name;

删除多列: ALTER TABLE tbl_name DROP col_name1,DROP col_name2;

修改数据表-添加约束

添加主键约束语法:

ALTER TABLE tbl_name ADD [CONSTRAINT [symbol]] PRIMARY KEY [index_type] (index_col_name,...)

创建一个新表:

mysql> CREATE TABLE users2(
    -> username VARCHAR(10) NOT NULL,
    -> pid SMALLINT UNSIGNED
    -> );
Query OK, 0 rows affected (0.09 sec)

添加一个字段:

mysql> ALTER TABLE users2 ADD id SMALLINT UNSIGNED;
Query OK, 0 rows affected (0.12 sec)
Records: 0  Duplicates: 0  Warnings: 0

添加主键:

mysql> ALTER TABLE users2 ADD CONSTRAINT PE_users2_id PRIMARY KEY (id);
Query OK, 0 rows affected (0.07 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> SHOW COLUMNS FROM users2;
+----------+----------------------+------+-----+---------+-------+
| Field    | Type                 | Null | Key | Default | Extra |
+----------+----------------------+------+-----+---------+-------+
| username | varchar(10)          | NO   |     | NULL    |       |
| pid      | smallint(5) unsigned | YES  |     | NULL    |       |
| id       | smallint(5) unsigned | NO   | PRI | NULL    |       |
+----------+----------------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

添加唯一约束:

mysql> ALTER TABLE users2 ADD UNIQUE (username);
Query OK, 0 rows affected (0.03 sec)
Records: 0  Duplicates: 0  Warnings: 0

添加/删除默认约束

ALTER TABLE tbl_name ALTER [COLUMN] col_name {SET DEFAULT literal | DROP DEFAULT}

修改数据表-删除约束

删除主键约束

语法:

ALTER TABLE tbl_name DROP PRIMARY KEY

删除唯一约束

语法:

ALTER TABLE tbl_name DROP {INDEX | KEY} index_name

修改数据表-修改列定义和更名数据库

修改列定义:

ALTER TABLE tbl_name MODIFY [COLUMN] col_name column_definition [FIRST | AFTER col_name]

数据表更名:

  • 方法1:ALTER TABLE tbl_name RENAME [TO | AS] new_tbl_name

  • 方法2: RENAME TABLE tbl_name TO new_tbl_name [, tbl_name2 TO new_tbl_name2] ...

总结

  • 约束
    • 功能
      • NOT NULL(非空约束)
      • PRIMARY KEY(主键约束)
      • UNIQUE KEY(唯一约束)
      • DEFAULT(默认约束)
      • FOREIGN KEY(外键约束)
    • 数据列的数目
      • 表级约束
      • 列级约束
  • 修改数据表
    • 针对字段的操作:添加/删除字段、修改列定义,修改列名称等;
    • 针对约束的操作:添加/删除各种约束
    • 针对数据表的操作:数据表更名(两种方式)

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