如何查看表列的所有外键？-mysql教程-PHP中文网

如何查看表列的所有外键？

要查看表或列的所有外键，referenced_column_name 命令是

首先，创建两个表，然后在外键约束的帮助下关联起来。

创建第一个表 -

mysql> CREATE table ForeignTable -> ( -> id int, -> name varchar(200), -> Fk_pk int -> ); Query OK, 0 rows affected (0.43 sec)

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成功创建第一个表后，创建第二个表如下 -

mysql> CREATE table primaryTable1 -> ( -> Fk_pk int, -> DeptName varchar(200), -> Primary key(Fk_pk) -> ); Query OK, 0 rows affected (0.48 sec)

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现在，两个表都在 alter 命令和外键的帮助下关联起来还添加了约束。其语法如下 -

alter table yourFirstTable add constraint anyConstraintName foreign key(column_name which is acts foreign key in second table) yourSecondTable(column_name which acts primary key in second table).

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上述语法用于关联两个表，如下 -

mysql> alter table ForeignTable add constraint constFKPK foreign key(Fk_pk) references primaryTable1(Fk_pk); Query OK, 0 rows affected (1.57 sec) Records: 0 Duplicates: 0 Warnings: 0

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现在，查看表的所有外键的语法如下 -

对于表 -

SELECT TABLE_NAME, COLUMN_NAME, CONSTRAINT_NAME, REFERENCED_TABLE_NAME, REFERENCED_COLUMN_NAME FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE WHERE REFERENCED_TABLE_NAME = 'yourReferencedTableName';

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现在使用上面的语法创建查询来查看所有外键。查询如下 -

mysql> SELECT TABLE_NAME, COLUMN_NAME, CONSTRAINT_NAME, REFERENCED_TABLE_NAME,REFERENCED_COLUMN_NAME -> FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE -> WHERE REFERENCED_TABLE_NAME = 'primarytable1';

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以下是输出 -

+--------------+-------------+-----------------+-----------------------+------------------------+ | TABLE_NAME | COLUMN_NAME | CONSTRAINT_NAME | REFERENCED_TABLE_NAME | REFERENCED_COLUMN_NAME | +--------------+-------------+-----------------+-----------------------+------------------------+ | foreigntable | Fk_pk | constFKPK | primarytable1 | fk_pk | +--------------+-------------+-----------------+-----------------------+------------------------+ 1 row in set, 2 warnings (0.02 sec)

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在示例输出中，constraint_name 为“constFKPK”，table_name 为“foreigntable”。对于一列 -

SELECT TABLE_NAME,COLUMN_NAME,CONSTRAINT_NAME, REFERENCED_TABLE_NAME,REFERENCED_COLUMN_NAME FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE WHERE REFERENCED_TABLE_SCHEMA = 'yourDatabaseName' AND REFERENCED_TABLE_NAME = 'yourreferencedtablename' AND REFERENCED_COLUMN_NAME = 'yourreferencedcolumnname';

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使用上述语法给出显示列的所有外键的查询。查询如下如下 -

mysql> SELECT -> TABLE_NAME,COLUMN_NAME,CONSTRAINT_NAME, REFERENCED_TABLE_NAME,REFERENCED_COLUMN_NAME -> FROM -> INFORMATION_SCHEMA.KEY_COLUMN_USAGE -> WHERE -> REFERENCED_TABLE_SCHEMA = 'business' AND -> REFERENCED_TABLE_NAME = 'primarytable1' AND REFERENCED_COLUMN_NAME = 'fk_pk';

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得到的输出如下：

+--------------+-------------+-----------------+-----------------------+------------------------+ | TABLE_NAME | COLUMN_NAME | CONSTRAINT_NAME | REFERENCED_TABLE_NAME |REFERENCED_COLUMN_NAME | +--------------+-------------+-----------------+-----------------------+------------------------+ | foreigntable | Fk_pk | constFKPK | primarytable1 | fk_pk | +--------------+-------------+-----------------+-----------------------+------------------------+ 1 row in set, 2 warnings (0.03 sec)

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