要查看表或列的所有外鍵,referenced_column_name 指令是
首先,建立兩個表,然後在外鍵約束的幫助下關聯起來。
建立第一個表-
mysql> CREATE table ForeignTable -> ( -> id int, -> name varchar(200), -> Fk_pk int -> ); Query OK, 0 rows affected (0.43 sec)
成功建立第一個表後,建立第二個表如下-
mysql> CREATE table primaryTable1 -> ( -> Fk_pk int, -> DeptName varchar(200), -> Primary key(Fk_pk) -> ); Query OK, 0 rows affected (0.48 sec)
現在,兩個表都在alter 指令和外鍵的幫助下關聯起來 也添加了約束。其語法如下-
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).
上述語法用於關聯兩個表,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
#現在,查看表的所有外鍵的語法如下-
#對於表-
SELECT TABLE_NAME, COLUMN_NAME, CONSTRAINT_NAME, REFERENCED_TABLE_NAME, REFERENCED_COLUMN_NAME FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE WHERE REFERENCED_TABLE_NAME = 'yourReferencedTableName';
現在使用上面的語法建立查詢來查看所有外鍵。查詢如下 -
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';
以下是輸出 -
+--------------+-------------+-----------------+-----------------------+------------------------+ | 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)
在範例輸出中,constraint_name 為“constFKPK”,table_name 為“foreigntable”。 對於一列 -
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';
使用上述語法給予顯示列的所有外鍵的查詢。查詢如下 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';
得到的輸出如下:
+--------------+-------------+-----------------+-----------------------+------------------------+ | 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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