Answers for "laravel remove constraint using query"

laravel migration remove unique constraint

/** To drop an index you must specify the index's name. 
Laravel assigns a reasonable name to the indexes by default. 
Simply concatenate the table name, the names of the column in the index, 
and the index type **/

// Format of unique key tableName_column_unique
$table->dropUnique('users_email_unique');

remove foreign key constraint laravel

Schema::table('table_name', function (Blueprint $table) {
    $table->dropForeign(['foreign_key']);
    $table->dropColumn('column_key');
});

PS: usually foreign_key = column_key

ex: 

Schema::table('despatch_discrepancies', function (Blueprint $table) {
    $table->dropForeign(['pick_detail_id']);
    $table->dropColumn('pick_detail_id');
});