Tag Archives: LOOP

How to use a while loop to iterate through each table of each database within an instance

Say you have code you want executed against every table on a SQL Server instance, you could use SQL Server’s inbuilt sp_MSForEachDB and sp_MSForEachTable. I’m not a big fan of them though because they are undocumented, so I’d always be concerned Microsoft might decide to kill it with any given patch or service pack update. (I know the likelihood of that is extremely low but I’m a risk adverse kinda guy)

I prefer to use the example below. It may not be the most efficient snippet of code available on the net but it’s good and simple and it’s not going anywhere unless I drop it.

SET NOCOUNT ON

DECLARE @Database TABLE (DbName SYSNAME)
DECLARE @DbName AS SYSNAME

SET @DbName = ''

INSERT INTO @Database (DbName)
SELECT NAME
FROM sys.databases
WHERE NAME <> 'tempdb'
AND state_desc = 'ONLINE'
ORDER BY NAME ASC

WHILE @DbName IS NOT NULL
BEGIN
	SET @DbName = (
			SELECT MIN(DbName)
			FROM @Database
			WHERE DbName > @DbName
			)

	/*
	PUT CODE HERE
	EXAMPLE PRINT Database Name
	*/
	PRINT @DbName
END

 

How to use a while loop to iterate through Databases

Say you have code you want executed against every database on a SQL Server instance, you could use SQL Server’s inbuilt sp_MSForEachDB. I’m not a big fan of it though because it is undocumented, so I’d always be concerned Microsoft might decide to kill it with any given patch or service pack update. (I know the likelihood of that is extremely low but I’m a risk adverse kinda guy)

I prefer to use the example below. It may not be the most efficient snippet of code available on the net but it’s good and simple and it’s not going anywhere unless I drop it.

(To execute code against every table in an instance see this post)

SET NOCOUNT ON

DECLARE @Database TABLE (DbName SYSNAME)
DECLARE @DbName AS SYSNAME

SET @DbName = ''

INSERT INTO @Database (DbName)
SELECT NAME
FROM master.dbo.sysdatabases
WHERE NAME <> 'tempdb'
ORDER BY NAME ASC

WHILE @DbName IS NOT NULL
BEGIN
	SET @DbName = (
			SELECT MIN(DbName)
			FROM @Database
			WHERE DbName > @DbName
			)

	/*
	PUT CODE HERE
	EXAMPLE PRINT Database Name
	*/
	PRINT @DbName
END

How to determine what stored procedures relate to what tables

Foreign keys are usually a good indicator of which tables connect to each other however you may be working in an environment that does not always follow best practices. As well as that you may not know what store procedures relate to what tables.
Sometimes databases need to move from one server to another or are depreciated. Before this can happened it is a very good idea to do a compressive assessment to see what interacts with what.
As once a thing gets moved everything that queries against it needs to point to it its new location.
A good starting point of this assessment would be to use the query below to determine what stored procedures reference the table specified in the WHERE clause.

  • NOTES: This query only pulls the tabled referenced in the database, it does not pull tables that are referenced from other databases.
  • Although the table maybe reference it may not actually be interacted with by the query, the table name may be comment in the code for example. However for the most part it is more likely the table has some action performed against it, be it a SELECT, INSERT, UPDATE etc.

The query works by using the sysobjects and syscomments tables.
Sysobjects: a system table that contains a row for each user-defined, schema-scoped object that is created within a database, including natively compiled scalar user-defined function.

Syscomments: a system table that contains entries for each view, rule, default, trigger, CHECK constraint, DEFAULT constraint, and stored procedure within the database. The text column contains the original SQL definition statements.

Or to dumb it down it joins, in our case, the stored procedures name to the query and scans this query for references to the specified table.

/*
CHANGE THE FOLLOWING:
SERVER NAME: ServerName
DATABASE NAME: DatabaseName 
TABLE NAME: TableName
 */


USE DatabaseName;
GO

SELECT DISTINCT so.name
FROM syscomments sc
INNER JOIN sysobjects so ON sc.id=so.id
WHERE sc.TEXT LIKE '%TableName%'

To expand on this logic to return every table referenced in every stored procedure in a database run the code below:

/*
CHANGE THE FOLLOWING:
SERVER NAME: ServerName
DATABASE NAME: DatabaseName 
 */
 
USE DatabaseName;
GO 

--DROP TEMP TABLES
IF OBJECT_ID('tempdb..#TablesAndSPs') IS NOT NULL
	DROP TABLE #TablesAndSPs

IF OBJECT_ID('tempdb..#Tables') IS NOT NULL
	DROP TABLE #Tables
	
--DECLARE VARIABLES
DECLARE @tableID AS INT
DECLARE @tableName AS VARCHAR(255)

--CREATE TEMP TABLE TO HOLD THE NAMES OF THE TABLES AND SPs
CREATE TABLE #TablesAndSPs (
	TABLE_ID INT
	,TABLE_NAME VARCHAR(255)
	,SP VARCHAR(255)
	)

--GET A LIST OF THE TABLES IN DATABASE
SELECT row_number() OVER (
		ORDER BY TABLE_NAME
		) AS TABLE_ID
	,TABLE_NAME
INTO #Tables
FROM INFORMATION_SCHEMA.TABLES

SET @tableID = 1

--LOOP AND POPULATE #TablesAndSPs
WHILE @tableID <= (
		SELECT MAX(TABLE_ID)
		FROM #Tables
		)
BEGIN
	SET @tableName = (
			SELECT TABLE_NAME
			FROM #Tables
			WHERE TABLE_ID = @tableID
			)

	INSERT INTO #TablesAndSPs
	SELECT DISTINCT @tableID
		,@tableName
		,so.NAME
	FROM syscomments sc
	INNER JOIN sysobjects so ON sc.id = so.id
	WHERE sc.TEXT LIKE '%' + @tableName + '%'

	SET @tableID = @tableID + 1
END

SELECT * FROM #TablesAndSPs

Distinct Row Count Table

If you come from a programming background you might want to do a loop using TSQL rather than using a cursor.

The syntax for this is pretty recognisable, exempli gratia,

However if you want to feed in dynamic variables captured from a table you can create a distinctive row count table.

This deduplicates the occurrence of a field value and assigns it a row number.

Where this can be used will be included in a more complicated example coming in the future.