loop script is not working - sql

Question

I'm just trying to create tables in user databases apart from system databases.
here is the script
Declare #V table (ID INT,name varchar(100))
DECLARE
#DatabaseName VARCHAR(50),
#SQL NVARCHAR(MAX)
INSERT INTO #V(Id,name)
select ROW_NUMBER()OVER(ORDER BY NAME),
name
from sys.databases
where database_id >= 5
DECLARE #LoopCounter INT , #MaxId INT,
#Name NVARCHAR(100)
SELECT #LoopCounter = min(id) ,
#MaxId = max(Id)
FROM #V
WHILE(#LoopCounter IS NOT NULL
AND #LoopCounter <= #MaxId)
BEGIN
SELECT #Name = Name
FROM #V WHERE Id = #LoopCounter
set #Name = #DatabaseName
SET #SQL = N'USE ' + QUOTENAME(#DatabaseName)
+'CREATE TABLE T(ID INT)';
SET #LoopCounter = #LoopCounter + 1
-- PRINT(#DatabaseName);
--PRINT(#SQL);
EXECUTE(#SQL)
END
why is it not creating table dynamically?
how to get only user databases in below script
instead of giving manually
DECLARE #Sql AS VARCHAR(4000)
SET #Sql = 'IF ''?'' NOT IN (''master'',''tempdb'',''model'',''msdb'',''ReportServer'',''ReportServerTempDB'')
EXECUTE (''
USE [?] CREATE TABLE T (ID INT)'')'
EXEC sp_MSforeachdb
#command1 = #Sql

Answer 1

The problems with your script are here:
WHILE(#LoopCounter IS NOT NULL
AND #LoopCounter <= #MaxId)
BEGIN
SELECT #Name = Name
FROM #V WHERE Id = #LoopCounter
--set #Name = #DatabaseName -- this will assign value from #DatabaseName into #Name, but you should do the vice versa:
set #DatabaseName = #Name
SET #SQL = N'USE ' + QUOTENAME(#DatabaseName)
+' CREATE TABLE T(ID INT)'; -- I would also add space here, it might work with [XXX]create table
SET #LoopCounter = #LoopCounter + 1
-- PRINT(#DatabaseName);
--PRINT(#SQL);
EXECUTE(#SQL)
END
Because #DatabaseName was null, the result of your #SQL was null, and executing null is most likely just ok.

Answer 2

Your draft of the version with the sp_MSforeachdb procedure was also fine; you asked for a version without writing the names of the system databases. Unfortunately this has still not been implemented - there is no reliable flag or property on a database that would clearly identify it as a user database. Microsoft themselves apply the (inverted) criteria I am using below, when they list the contents of the "System Databases" folder in SSMS... see also here: https://stackoverflow.com/a/28590305/1132334
SELECT
[name]
FROM sys.databases
WHERE CAST(CASE WHEN [name] IN ('master','model','msdb','tempdb') THEN 1 ELSE is_distributor END AS bit)=0
Here is a tested script:
DECLARE #sql varchar(max)
SET #sql='IF ''?'' IN (SELECT [name] FROM sys.databases WHERE CAST(CASE WHEN [name] IN (''master'',''model'',''msdb'',''tempdb'') THEN 1 ELSE is_distributor END AS bit)=0)
EXECUTE (''USE [?] CREATE TABLE T (ID int)'')'
EXEC sp_MSforeachdb #command1 = #Sql