SQLSTATE[23000]: Integrity constraint violation: 1022 Can't write; duplicate key in table

• Pivot table migration with custom constraint name

  --PATH database\migrations\<yourmigrationfile>.php

  //Migration command to create migration file
  php artisan make:migration create_role_user_table --create=role_user
  
  //Migration file code under - database\migrations\<yourmigrationfile>.php
  
  public function up()
  {
      Schema::create('role_user', function (Blueprint $table) {
          $table->foreignId('role_id')->constrained();
          $table->foreignId('user_id')->constrained();
          $table->foreign('user_id', 'fk_user_id')->references('id')->on('users')->onDelete('cascade');
          $table->foreign('role_id', 'fk_role_id')->references('id')->on('roles')->onDelete('cascade');
          $table->primary(['user_id', 'role_id']);
          $table->timestamps();
      });
  }
  

  This code snippet is helpful if you are getting SQLSTATE[23000]: Integrity constraint violation: 1022 Can't write; duplicate key in table Error while migration. You can create a table with your own custom constraint keyname. Laravel uses the default constraint naming convention to create a constraint name if you did not pass the value to $table->foreign() method. Here we pass (fk_user_id) as constraint name as own custom constraint name.

  
  You can also run SQL query to get the table schema and table name if their constraint exists. Just replace the value instead of 'role_user_role_id_foreign', 'role_user_user_id_foreign' as per your constraint name.
  SELECT `TABLE_SCHEMA`, `TABLE_NAME` FROM `information_schema`.`KEY_COLUMN_USAGE` WHERE `CONSTRAINT_NAME` IN ('role_user_role_id_foreign', 'role_user_user_id_foreign').

• Add constraint in existing table in MySQL

  //Add constraint in an existing table
  ALTER TABLE role_user ADD CONSTRAINT fk_role_id FOREIGN KEY (role_id) REFERENCES roles (id);
  
  //If you are getting an error Can't write; duplicate key in table '#sql-15fc_475' and want to use the same constraint name which already exists then first drop the existing foreign key and index, after that run the above query to create the constraint name.
  // Drop constraint in MySQL
  ALTER TABLE role_user DROP FOREIGN KEY fk_role_id; 
  ALTER TABLE role_user DROP INDEX fk_role_id;
  

  This code snippet adds the constraint fk_role_id on the role_user table with references on the roles table’s id. If you are getting the error Can't write; duplicate key in table '#sql-15fc_475' while executing MySQL query that means constraint with name fk_role_id already exists then you have to change the constraint name instead of ‘fk_role_id’, use ‘fknew_role_id’ or as per your requirement.  

  If you want to use the same constraint name which already exists then first drop the existing constraint and run add constraint SQL query to create constraint. There is no SQL query to drop constraint in MySQL. You have to drop foreign key and index and after that, you can add a constraint to create a constraint with this specific name.

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