Extracting stored procedure source text from SQL Server

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It’s been a really long time since the last post so here’s a small SQL Server tip. I recently had to extract the source code for more than two hundred stored procedures from a SQL Server database. Obviously I didn’t want to do that by hand so I wrote a simple script using sp_helptext:

exec sp_helptext proc1
exec sp_helptext proc2
exec sp_helptext proc3
...

This did indeed extract all the source code for the procs but for some obscure reason I had a newline character after every 255:th character in the result. Close but no cigar…

I did some googling without finding anyone with the identical problem (I had already increased the “Maximum number of characters displayed in each column” setting of SQL Server Management Studio). However, it turns out there’s an alternative to sp_helptext, namely the sys.sql_modules table which can be queried like this:

select definition from sys.sql_modules where object_id = object_id('proc1')
select definition from sys.sql_modules where object_id = object_id('proc2')
select definition from sys.sql_modules where object_id = object_id('proc3')
...

This time there were no irritating newlines in the output. Problem solved!

/Emil

Unique constraints in Sql Server do not allow multiple NULL values

For some obscure reason Sql Server does not allow multiple NULL values on columns with UNIQUE constraints. This is in conflict with ANSI standards and also very contra-intuitive.

If you think this is poorly designed, you’re not alone: http://connect.microsoft.com/SQLServer/feedback/details/299229/change-unique-constraint-to-allow-multiple-null-values

However, there is a way to create a constraint that allows multiple NULL values rather easily (this uses “filtered constraints”, introduced in Sql Server 2008):

CREATE UNIQUE NONCLUSTERED INDEX idx_yourcolumn_notnull
ON YourTable(yourcolumn)
WHERE yourcolumn IS NOT NULL;

Credits: http://stackoverflow.com/questions/767657/how-do-i-create-unique-constraint-that-also-allows-nulls-in-sql-server

/Emil

Storing and retrieving strings in the SQL Server session context

Sometimes it can be useful to store temporary data (e.g. a string with the current username for auditing or similar) in the context of the current Sql Server session and it’s actually rather easy to do. All that’s needed is to convert the data to a varbinary of max length 128 and then call SET CONTEXT_INFO like this:

-- store data
DECLARE @encodedUsername AS VARBINARY(128)
SET @encodedUsername = convert(varbinary(128),'emila')
SET CONTEXT_INFO @encodedUsername

Unfortunately it’s not quite as easy to retrieve the original string… You can retrieve the varbinary data using CONTEXT_INFO(), but that will only give the varbinary data back:

SELECT CONTEXT_INFO()

0x656D696C610000000000000...

Converting that data back to a varchar seems to work at first but the string contains trailing 0-characters (cf. CHAR(0) ):

-- Convert to a string, looks ok...
SELECT CONVERT(VARCHAR(MAX), CONTEXT_INFO())
emila

-- ... but the length is 128 characters
SELECT LEN(CONVERT(VARCHAR(MAX), CONTEXT_INFO()))
128

Removing those illegal character is surprisingly difficult (e.g. REPLACE() cannot be used) but one possible solution is to do a conversion into an Xml string:

-- convert to xml for 
SELECT CONVERT(VARCHAR(MAX), (SELECT CONVERT(VARCHAR(MAX), CONTEXT_INFO()) AS data FOR XML PATH('')))
<data>emila&#x00;&#x00;&#x00;&#x00;&#x00;&#x00;&#x00;...

Substrings of that Xml string can then be replaced like in any other string and that logic is best put in a user-defined function:

-- Retrieve data from the context and cleanup illegal characters
CREATE FUNCTION GetLoggedInUserName() RETURNS varchar(20)
AS
  BEGIN
    RETURN
      REPLACE(
        REPLACE(
          REPLACE(
            CONVERT(VARCHAR(MAX), (SELECT CONVERT(VARCHAR(MAX), CONTEXT_INFO()) AS data FOR XML PATH('')))
            , '</data><data>', '')
          , '</data>', '')
        , '&#x00;', '')
  END
GO


SELECT dbo.GetLoggedInUserName()
emila

The result is now a string of the correct length and without illegal characters.

This code works as expected, but perhaps there is a more efficient alternative out there? Please leave a comment if you have a suggestion for improvement 🙂

/Emil

Templates for SQL Server Management Studio

Templates for SQL Server Management Studio 2008 are stored in this folder on WIndows XP:

C:\Documents and Settings\[user]\Application Data\Microsoft\Microsoft SQL Server\100\Tools\Shell\Templates\Sql

On my new WIndows 7 machine, the location is:

C:\Users\[user]\AppData\Roaming\Microsoft\Microsoft SQL Server\100\Tools\Shell\Templates\Sql

Create sub-folders and SQL files there and they show up in the Template Explorer. Really useful…

/Emil

Finding dependencies on a table column

This will list stored procedures, views, etc. that uses a given table column:

SELECT OBJECT_NAME(sd.id) Dependent_Object,
      (SELECT xtype FROM sysobjects so WHERE so.id = sd.id) Object_Type
FROM sysobjects so
INNER JOIN syscolumns sc ON so.id = sc.id
INNER JOIN sysdepends sd  ON so.id = sd.depid and sc.colid = sd.depnumber
WHERE so.id = OBJECT_ID('tblcategorypage')
AND sc.name = 'categorytype'

Credits for this tip to SQLServerCentral.

/Emil

Bitwise operators in T-SQL?

You won’t need them very often but it might be good to know that they’re there. Here’s an example of how to use a bitwise AND in a where clause:

SELECT * FROM uppdrag WHERE (applikationer & 1) > 0

In this example, ‘applikationer’ is a column containing several combined flags and we want to check the setting on the flag in the lowest bit.

The bitwise operators are:

  • & – bitwise AND
  • | – bitwise OR
  • ^ – bitwise EXCLUSIVE OR

Easy way to create temporary tables in SQL Server

Have you ever had a need to create temporary database tables in a SQL Server session or procedure? Are you used to creating them by hand like this:

CREATE TABLE #tmp
( 
    id INT, 
    name VARCHAR(32) 
)

Depending on what you need the table for, then there might be an easier way. Have a look at this short session:

SELECT * INTO mytemptable FROM foobar
SELECT * FROM mytemptable
DROP TABLE mytemptable

The first line creates a new temporary table based on the result set of a SELECT query, and stores the result set in the table. The query can be more complex than in the example, with JOINs, WHERE clauses etc. Incredibly useful when mangling and transforming data!