Question

I have a new table that has foreign key references to a number of existing tables. When I create the new table for the first time, I created the foreign keys in the following way:

ALTER TABLE [dbo].[NewTable] WITH CHECK ADD FOREIGN KEY([SectionDatabaseID])
REFERENCES [dbo].[Section] ([SectionDatabaseID])

ALTER TABLE [dbo].[NewTable] WITH CHECK ADD FOREIGN KEY([TermDatabaseID])
REFERENCES [dbo].[Term] ([TermDatabaseID])

The above way will generate names for the foreign key constraints using it’s own automated naming convention.

However, I want to drop the new table because I need to do some major modifications by creating it from scratch.

Obviously, if I just execute a drop statement, the SQL Server database will complain stating that the new table has foreign key references to other tables.

I’ve heard of running the following script to figure out what foreign keys exist so that we can drop them:

use perls;
SELECT 'ALTER TABLE ' + TABLE_SCHEMA + '.[' + TABLE_NAME +
'] DROP CONSTRAINT [' + CONSTRAINT_NAME + ']'
FROM information_schema.table_constraints
WHERE CONSTRAINT_TYPE = 'FOREIGN KEY' and TABLE_NAME = 'NewTable'

The above will give results that basically show alter statements which I need to run.

I need something more automated. Why do I have to drop each foreign key constraint separately, and then only be able to drop the table?

I want to drop the table in a simpler way. It’s got to be easier than what I need to do above.

Answer 1

Yes you must drop the FKs first. I’ve ran into this before and have written just the script you need to automate the task. Replace DBName and TABLENAME below.

Warning to all: This script will drop a specific table (or group of tables) as well as all FK constraints! Use with caution, and always take a db backup before doing a major operation like this.

    use DBName
    /* 
    SCRIPT TO DROP TABLES WITH FK'S, INDEXES 
    https://mellodev.snipt.net/drop-tables-with-fk-contraints/
    */

    set nocount on

declare @tables table (tablename varchar(255));
insert into @tables
select name from sys.tables where name in 
('TABLENAME')

-- Iterate tables, drop FK constraints and tables
declare @tablename varchar(255);
declare cTable cursor for
select tablename from @tables
open cTable
fetch next from cTable into @tableName
while @@FETCH_STATUS=0
begin
    -- Identify any FK constraints
    declare @fkCount int;
    SELECT @fkCount = COUNT(*)
    FROM sys.foreign_keys
    WHERE referenced_object_id = object_id(@tablename)

    -- Drop any FK constraints from the table
    if (@fkCount>0) begin
        declare @dropFkSql nvarchar(max);set @dropFkSql='';
        declare @fkName nvarchar(max);
        declare cDropFk cursor for  
            SELECT 'ALTER TABLE [' + OBJECT_NAME(parent_object_id) + '] DROP CONSTRAINT [' + name + ']',name
            FROM sys.foreign_keys
            WHERE referenced_object_id = object_id(@tablename)
        open cDropFk
        fetch next from cDropFk into @dropfksql,@fkName
        while @@FETCH_STATUS=0
        begin       
            exec sp_executesql @dropFkSql;

            select 'Dropped FK Constraint: ' + @fkName
            fetch next from cDropFk into @dropfksql,@fkName
        end
        close cDropFk
        deallocate cDropFk          
    end

    -- Drop the table
    declare @dropTableSql nvarchar(max);
    set @dropTableSql='DROP TABLE [' + @tablename + ']';
    exec sp_executesql @dropTableSql;

    select 'Dropped table: ' + @tablename

    fetch next from cTable into @tableName
end
close cTable
deallocate cTable