Cannot drop index 'fk_role_id': needed in a foreign key constraint

• Drop constraint in MySQL

  // Drop constraint in MySQL
  ALTER TABLE role_user DROP FOREIGN KEY fk_role_id; 
  ALTER TABLE role_user DROP INDEX fk_role_id;
  

  No MySQL query exists to drop a constraint. Foreign keys in MySQL automatically create an index on the table. To drop the index ‘fk_role_id’ you have to first drop foreign key, after dropping foreign key you can run a drop query on the table in MySQL to drop the index.

  You can run the below SQL query to check constraint exists or not. You have to just change the name of constraint instead of 'fk_role_id'.

  SELECT `TABLE_SCHEMA`, `TABLE_NAME` FROM `information_schema`.`KEY_COLUMN_USAGE` WHERE `CONSTRAINT_NAME` IN ('fk_role_id')

   

• How to drop a constraint in Oracle?

  The syntax for dropping a unique constraint in Oracle is: ALTER TABLE table_name DROP CONSTRAINT constraint_name; table_name.

• How do you drop a foreign key constraint SQL server?

  To delete a foreign key constraint In Object Explorer, expand the table with the constraint and then expand Keys. Right-click the constraint and then click Delete.

• Does dropping a constraint drop the index?

  When you drop a constraint, any indexes created as a result of the constraint creation will be dropped. However, if you attempt to drop a unique or primary key constraint and there are foreign key constraints that reference it, you will get an error.

• Can we write a query to drop a foreign key constraint?

  To drop a foreign key from a table, use the ALTER TABLE clause with the name of the table (in our example, student ) followed by the clause DROP CONSTRAINT with the name of the foreign key constraint. In our example, the name of this constraint is fk_student_city_id (SQL).

• Is index required on foreign key?

  MySQL requires that foreign key columns be indexed; if you create a table with a foreign key constraint but no index on a given column, an index is created. Information about foreign keys on InnoDB tables can also be found in the INNODB_FOREIGN and INNODB_FOREIGN_COLS tables, in the INFORMATION_SCHEMA database.

• Do primary and foreign keys have indexes?

  Unlike primary key constraints, when a foreign key constraint is defined for a table, an index is not created by default by SQL Server. However, it's not uncommon for developers and database administrators to add them manually.

• Is foreign key always a primary key?

  Yes, foreign key has to be primary key of parent table.

• What is the use of primary key foreign key indexing in database?

  A primary key is used to ensure data in the specific column is unique. A foreign key is a column or group of columns in a relational database table that provides a link between data in two tables. It uniquely identifies a record in the relational database table.

• Can we delete foreign key without deleting primary key?

  To successfully change or delete a row in a foreign key constraint, you must first either delete the foreign key data in the foreign key table or change the foreign key data in the foreign key table, which links the foreign key to different primary key data.

• How to avoid cannot drop index 'fk_role_id': needed in a foreign key constraint error?

  When there is only one index that can be used for the foreign key, it can't be dropped. If you really wan't to drop it, you either have to drop the foreign key constraint or to create another index for it first.

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