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ALTER TABLE child_table_name ADD FOREIGN KEY (child_table_column) REFERENCES parent_table_name(parent_table_column); child_table_name is that table in which we want to add constraint. child_table_column is that table column in which we want to add foreign key.
The FOREIGN KEY constraint is used to prevent actions that would destroy links between tables. A FOREIGN KEY is a field (or collection of fields) in one table, that refers to the PRIMARY KEY in another table.
The following SQL command adds a Foreign Key to an existing table. ALTER TABLE Subject ADD FOREIGN KEY (StudentID) REFERENCES Student(StudentID); Drop foreign key MySQL. For dropping a Foreign key from a MySQL table, you need to know the name of the foreign key first. You can get the name of the foreign key by show create table command as follows.
1 sie 2010 · MySQL Workbench enables you to add a foreign key from within the table editor or from within an EER diagram by using the relationship tools on the vertical toolbar. This section describes how to add a foreign key using the foreign key tools.
15 lip 2013 · You need to add the CATEGORY_NAME column on ITEM TABLE, or map the foreign key to another existing column in ITEM. Either: ALTER TABLE ITEM ADD CATEGORY_NAME VARCHAR(35) NOT NULL; ALTER TABLE ITEM ADD CONSTRAINT FK_CATEGORY_NAME FOREIGN KEY (CATEGORY_NAME) REFERENCES CATEGORY (CATEGORY_NAME);
Summary: in this tutorial, you will learn about MySQL foreign key and how to create, drop, and disable a foreign key constraint. Introduction to MySQL foreign key. A foreign key is a column or group of columns in a table that links to a column or group of columns in another table.
To add a foreign key, click the last row in the Foreign Key Name list. Enter a name for the foreign key and select the column or columns that you wish to index by checking the column name in the Column list.
