How to Generate Table Create Script in T-SQL

dynamic-sqlsql serversql-server-2012t-sql

Is there a way to generate a create script from an existing table purely in T-SQL (that is without using SMO, since T-SQL does not have access to SMO). Let's say a stored procedure that receives a table name and returns a string that contains the create script for the given table?

Now let me describe the situation I'm facing, as there may be a different way to approach this. I have an instance with several dozen databases. These database all have the same schema, all the same tables, index and so on. They were created as a part of a third party software installation. I need to have a way to work with them so that I can aggregate data from them in ad-hoc manner. Nice people at dba.se have already helped me here How to create a trigger in a different database?

Currently I need to find a way to make a select from a table across all the databases. I have recorded all the database names into a table called Databasees and I wrote the following script to execute a select statement on all of them:

IF OBJECT_ID('tempdb..#tmp') IS NOT NULL
DROP TABLE #tmp

select * into #tmp from Database1.dbo.Table1 where 1=0
DECLARE @statement nvarchar(max) = 
  N'insert into #tmp select * from Table1 where Column1=0 and Cloumn2 =1'

DECLARE @LastDatabaseID INT
SET @LastDatabaseID = 0

DECLARE @DatabaseNameToHandle varchar(60)
DECLARE @DatabaseIDToHandle int

SELECT TOP 1 @DatabaseNameToHandle = Name,
@DatabaseIDToHandle = Database_Ref_No
FROM Databasees
WHERE Database_Ref_No > @LastDatabaseID
ORDER BY Database_Ref_No

WHILE @DatabaseIDToHandle IS NOT NULL
BEGIN

  DECLARE @sql NVARCHAR(MAX) = QUOTENAME(@DatabaseNameToHandle) + '.dbo.sp_executesql'
  EXEC @sql @statement

  SET @LastDatabaseID = @DatabaseIDToHandle
  SET @DatabaseIDToHandle = NULL

  SELECT TOP 1 @DatabaseNameToHandle = Name,
  @DatabaseIDToHandle = Database_Ref_No
  FROM Databasees
  WHERE Database_Ref_No > @LastDatabaseID
  ORDER BY Database_Ref_No
END

select * from #tmp
DROP TABLE #tmp

However the script above fails with the following message:

An explicit value for the identity column in table '#tmp' can only be
specified when a column list is used and IDENTITY_INSERT is ON.

Adding this:

SET IDENTITY_INSERT #tmp ON

does not help, since, I can't specify the column list and keep it generic.

In SQL there is no way to switch the identity on a given table off. You can only drop a column and add a column, which, obviously changes the column order. And if the column order changes, you, again, need to specify the column list, that would be different depending on the table you query.

So I was thinking if I could get the create table scrip in my T-SQL code, I could manipulate it with string manipulation expressions to remove the identity column and also add a column for the Database name to the result set.

Can anyone think of a relatively easy way to achieve what I want?

Best Answer

Back in 2007, I asked for an easy way to generate a CREATE TABLE script via T-SQL rather than using the UI or SMO. I was summarily rejected.

However, SQL Server 2012 makes this very easy. Let's pretend we have a table with the same schema across multiple databases, e.g. dbo.whatcha:

CREATE TABLE dbo.whatcha
(
  id INT IDENTITY(1,1), 
  x VARCHAR(MAX), 
  b DECIMAL(10,2), 
  y SYSNAME
);

The following script uses the new sys.dm_exec_describe_first_results_set dynamic management function to retrieve the proper data types for each of the columns (and ignoring the IDENTITY property). It builds the #tmp table you need, inserts from each of the databases in your list, and then selects from #tmp, all within a single dynamic SQL batch and without using a WHILE loop (that doesn't make it better, just simpler to look at and allows you to ignore Database_Ref_No entirely :-)).

SET NOCOUNT ON;

DECLARE @sql NVARCHAR(MAX), @cols NVARCHAR(MAX) = N'';

SELECT @cols += N',' + name + ' ' + system_type_name
  FROM sys.dm_exec_describe_first_result_set(N'SELECT * FROM dbo.whatcha', NULL, 1);

SET @cols = STUFF(@cols, 1, 1, N'');

SET @sql = N'CREATE TABLE #tmp(' + @cols + ');'

DECLARE @dbs TABLE(db SYSNAME);

INSERT @dbs VALUES(N'db1'),(N'db2');
  -- SELECT whatever FROM dbo.databases

SELECT @sql += N'
  INSERT #tmp SELECT ' + @cols + ' FROM ' + QUOTENAME(db) + '.dbo.tablename;'
  FROM @dbs;

SET @sql += N'
  SELECT ' + @cols + ' FROM #tmp;';

PRINT @sql;
-- EXEC sp_executesql @sql;

The resulting PRINT output:

CREATE TABLE #tmp(id int,x varchar(max),b decimal(10,2),y nvarchar(128));
  INSERT #tmp SELECT id,x,b,y FROM [db1].dbo.tablename;
  INSERT #tmp SELECT id,x,b,y FROM [db2].dbo.tablename;
  SELECT id,x,b,y FROM #tmp;

When you are confident it's doing what you expect, just uncomment the EXEC.

(This trusts you that the schema is the same; it does not validate that one or more of the tables has since been changed, and may fail as a result.)

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