Truncate all the tables in a Database in SQL Server - SQL Server / TSQL Tutorial Part 55

Scenario:

Let's think about a database that we use for our ETL process and we call that database staging. We want to truncate all the tables in morning so those can be used for the daily process. Once way is to write our Truncate statement for each of the table but tables can be dropped or new tables can be created as well. We want to write a query that we can be use to Truncate all the tables from a database and we don't have to rewrite our Truncate statements.

If the tables do not have Primary Key -Foreign Key relationship, we can use Truncate. But we often have tables which are referenced by other tables. We can not use Truncate statement for those tables. The only way to Truncate those tables is to drop the Foreign Key Constraint before Truncating and then Truncate and Recreate Relationship after that.

The below Code can be used to Truncate all the tables from the database. If Tables will have the Pk-Fk relationship, The script will drop the Foreign Key Constraints first and then Truncate those tables and finally recreate the Foreign Key constraints.

Before you run below Script, Make sure you are pointing to correct Database and Server! All the best with Truncating all the tables from a SQL Server Database.


-- Drop Temp Tables if Exists
 IF OBJECT_ID('tempdb..#DropConstraint') IS NOT NULL
  DROP TABLE #DropConstraint
 IF OBJECT_ID('tempdb..#CreateConstraint') IS NOT NULL
  DROP TABLE #CreateConstraint
 IF OBJECT_ID('tempdb..#TempTruncateTables') IS NOT NULL
    DROP TABLE #TempTruncateTables

-- Drop Constraint Script Save in #DropConstraint Temp Table 
SELECT 'ALTER TABLE ' + '['
       + Schema_name(o.schema_id) + '].['
       + OBJECT_NAME(FK.parent_object_id) + ']'
       + ' DROP  CONSTRAINT ' + '[' + FK.name + ']' AS DropConstraintQuery
 INTO   #DropConstraint
 FROM   sys.foreign_keys AS FK
       INNER JOIN sys.foreign_key_columns AS FKC
               ON FK.OBJECT_ID = FKC.constraint_object_id
       INNER JOIN sys.objects O
               ON O.OBJECT_ID = FKC.parent_object_id

-- Create Constraint Script Save in #CreateConstraint Temp Table 
SELECT 'ALTER TABLE ' + '['
       + Schema_name(o.schema_id) + '].' + '['
       + OBJECT_NAME(FK.parent_object_id) + ']'
       + ' ADD CONSTRAINT ' + '[' + FK.name
       + '] Foreign Key (['
       + (SELECT name
          FROM   sys.columns c
          WHERE  c.OBJECT_ID = FKC.parent_object_id
                 AND c.column_id = FKC.parent_column_id)
       + ']) REFERENCES ' + '['
       + Schema_name(o.schema_id) + '].['
       + (SELECT name
          FROM   sys.objects o
          WHERE  OBJECT_ID = FKC.referenced_object_id)
       + '] (['
       + (SELECT name
          FROM   sys.columns c
          WHERE  c.OBJECT_ID = FKC.referenced_object_id
                 AND c.column_id = FKC.referenced_column_id)
       + '])' AS CreateConstraintQuery
 INTO   #CreateConstraint
 FROM   sys.foreign_keys AS FK
       INNER JOIN sys.foreign_key_columns AS FKC
               ON FK.OBJECT_ID = FKC.constraint_object_id
       INNER JOIN sys.objects o
               ON FKC.parent_object_id = o.OBJECT_ID

-- Build Truncate Statement for all the tables and save into #TempTruncateTables
 SELECT 'Truncate table ' + Schema_name(schema_id)
       + '.' + name AS TruncateTableQuery
 INTO   #TempTruncateTables 
FROM   sys.tables
 WHERE  TYPE = 'U'
       AND is_ms_shipped = 0

GO

-- Drop Constraints
 DECLARE @DropConstraintQuery AS VARCHAR(4000)
 DECLARE DropConstraintCur CURSOR FOR
  SELECT DropConstraintQuery
  FROM   #DropConstraint
 OPEN DropConstraintCur 
FETCH Next FROM DropConstraintCur 
 INTO @DropConstraintQuery
 WHILE @@FETCH_STATUS = 0
  BEGIN
      DECLARE @SQL VARCHAR(MAX)=NULL
      SET @SQL=@DropConstraintQuery
      EXEC (@SQL)
      PRINT ' Query ::' + @DropConstraintQuery
            + 'Completed'
      FETCH Next FROM DropConstraintCur INTO @DropConstraintQuery
  END
CLOSE DropConstraintCur 
DEALLOCATE DropConstraintCur
GO-- Truncate tables 
DECLARE @TempTruncateTablesCur AS VARCHAR(4000) 
DECLARE TempTruncateTablesCur CURSOR FOR
  SELECT TruncateTableQuery
  FROM   #TempTruncateTables 
OPEN TempTruncateTablesCur
 FETCH Next FROM TempTruncateTablesCur 
 INTO @TempTruncateTablesCur
 WHILE @@FETCH_STATUS = 0
  BEGIN
      DECLARE @SQL VARCHAR(MAX)=NULL

      SET @SQL=@TempTruncateTablesCur

      EXEC (@SQL)

      PRINT ' Query ::' + @TempTruncateTablesCur
            + 'Completed'
      FETCH Next FROM TempTruncateTablesCur INTO @TempTruncateTablesCur
  END
CLOSE TempTruncateTablesCur 
DEALLOCATE TempTruncateTablesCur
GO


-- Create Constraint After Truncate 
DECLARE @CreateConstraintQuery AS VARCHAR(4000) 
DECLARE CreateConstraintQueryCur CURSOR FOR
  SELECT CreateConstraintQuery
  FROM   #CreateConstraint
 OPEN CreateConstraintQueryCur 
FETCH Next FROM CreateConstraintQueryCur 
 INTO @CreateConstraintQuery 
WHILE @@FETCH_STATUS = 0
  BEGIN
      DECLARE @SQL VARCHAR(MAX)=NULL
      SET @SQL=@CreateConstraintQuery
      EXEC (@SQL)
      PRINT ' Query ::' + @CreateConstraintQuery
            + 'Completed'
      FETCH Next FROM CreateConstraintQueryCur INTO  @CreateConstraintQuery
  END
CLOSE CreateConstraintQueryCur
 DEALLOCATE CreateConstraintQueryCur

GO 



Things we covered in this Post

• How to drop temp table if exists in SQL Server
• How to use system tables to get Primary key and foreign key Constraint
• How to use Cursors in SQL Server 
• How to Drop Foreign Key Constraints dynamically and Recreate them
• How to Truncate all tables in SQL Server Database
• How to use Dynamic SQL in TSQL
• How to use Variables in TSQL