Remove Foreign Key Relationships From All Tables

Question

I have a database that has several tables. Many of the tables have fields with foreign key constraints. I want to truncate the tables and then repopulate them with new data, and I also want to take off the foreign keys, as some of the relationships have changed. basically, I want to build the FK constraints up from scratch again. How can I remove the current FK constraints from all tables?

Answer 1

You can play with the information_schema. Take a look at this page

http://dev.mysql.com/doc/refman/5.0/en/key-column-usage-table.html

select concat('alter table ',table_name,' drop foreign key ',constraint_name,';') 
from information_schema.key_column_usage
where constraint_schema = 'your_db' and referenced_table_name = 'table_name';

then run the output generated.

You can do something similar in order to truncate all tables.

select concat('truncate ',table_name,';') 
from information_schema.tables
where table_schema = 'your_db' and table_type = 'base table'

this one will truncate all tables within the specified database. So use it with care.

Answer 2

I"m guessing you already found a solution, since this post is six months old, but I recently had to come up with a script to drop foreign key constraints to a particular table in MySQL, so that may help anyone else in the same boat:

# create a handy dandy stored procedure
DELIMITER $$
CREATE PROCEDURE DropConstraints(refschema VARCHAR(64), reftable VARCHAR(64), refcolumn VARCHAR(64))
BEGIN
    WHILE EXISTS(
        SELECT * FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE
        WHERE 1
        AND REFERENCED_TABLE_SCHEMA = refschema
        AND REFERENCED_TABLE_NAME = reftable
        AND REFERENCED_COLUMN_NAME = refcolumn
    ) DO
        BEGIN
            SET @sqlstmt = (
                SELECT CONCAT('ALTER TABLE ',TABLE_SCHEMA,'.',TABLE_NAME,' DROP FOREIGN KEY ',CONSTRAINT_NAME)
                FROM INFORMATION_SCHEMA.KEY_COLUMN_USAGE
                WHERE 1
                AND REFERENCED_TABLE_SCHEMA = refschema
                AND REFERENCED_TABLE_NAME = reftable
                AND REFERENCED_COLUMN_NAME = refcolumn
                LIMIT 1
            );
            PREPARE stmt1 FROM @sqlstmt;
            EXECUTE stmt1;
        END;
    END WHILE;
END$$
DELIMITER ;

To run it, simply use:

SET @schema = 'schema_name';
CALL DropConstraints(@schema, 'TableName', 'Referenced_Column_1');
CALL DropConstraints(@schema, 'TableName', 'Referenced_Column_2');

And if you don't want to keep the procedure around:

DROP PROCEDURE DropConstraints;

Of course if you want to drop all FK constraints to the table, you can remove the refcolumn parameter and the last line of each where clause.