Stairway to T-SQL: Beyond The Basics Level 9: Dynamic T-SQL Code

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Stairway to T-SQL: Beyond The Basics Level 9: Dynamic T-SQL Code

Greg Larsen

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Points: 20961
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July 8, 2014 at 7:26 pm

#308881

Comments posted to this topic are about the item Stairway to T-SQL: Beyond The Basics Level 9: Dynamic T-SQL Code
Gregory A. Larsen, MVP

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h.tobisch SSCommitted Points: 1671 More actions · Answer 1

Hi Greg,

I do not go quite with your conclusions.

If parameterized SQL is used as it is intended, the skeleton of the statement @CMD provided by the application and user input used only for parameters,

there will be no danger of SQL injection and consequently no advantage in avoiding dynamic SQL.

Concluding from what I know and what is stated in the article.

reagrds

Herbert

timwell SSCertifiable Points: 5315 More actions · Answer 2

Hello Greg,

Another good article. I have enjoyed this stairway series.

In this article I noticed a few inconsistencies that may be from changing your examples?

Several places you use "DELETE" where maybe it should be "DROP" or "DROP TABLE"?

You refer in some captions to a stored procedure called "GetUserName" and in the text to an @EMAIL parameter

Also it looks like this sentence: "In this example I deleted the Client table." should read "In this example I dropped the Product table."

fregatepllada SSCommitted Points: 1702 More actions · Answer 3

Greg, thank you for article.

Could you please refrain from providing SELECT * FROM table example - it's a proverbial ticking "time bomb".

Changes in table schema like creating new or dropping existing column could trigger a chain reaction of bug further down stream in middle-tier and/or on UI. My favorite anti-pattern - combining SELECT * with querying system views EVERY time somebody try to retrieve data. in this scenario even renaming a column could be a potential problem.

Robert.Sterbal SSCrazy Points: 2855 More actions · Answer 4

Do the cursors in the example of looping dynamic sql act as an implicit go statement?

Eirikur Eiriksson SSC Guru Points: 182912 More actions · Answer 5

Robert.Sterbal (7/24/2014)
Do the cursors in the example of looping dynamic sql act as an implicit go statement?

Yes, unless it is wrapped in an explicit transaction.

😎

Eirikur Eiriksson SSC Guru Points: 182912 More actions · Answer 6

Thanks Gregory for this nice peace, good job!

Missed seeing one essential thing though in the injection part and that is a strong coupling to the metadata. If a user can select in any form the objects (table/view/procedure etc.) to use, one should do a firm check for it's existence. A quick sample would be

😎

DECLARE @SCHEMA NVARCHAR(128) = N'dbo';

DECLARE @TABLE NVARCHAR(128) = N'CLIENT';

DECLARE @COLUMN NVARCHAR(128) = N'CLIENT_NAME';

DECLARE @SQL_STR NVARCHAR(MAX) = N''

SELECT

@SQL_STR = N'SELECT ' +

COLUMN_NAME

+ N' FROM ' + TABLE_SCHEMA

+ NCHAR(46) + TABLE_NAME

FROM INFORMATION_SCHEMA.COLUMNS

WHERE COLUMN_NAME = @COLUMN

AND TABLE_NAME = @TABLE

AND TABLE_SCHEMA = @SCHEMA

--- and so on

Luis Cazares SSC Guru Points: 183706 More actions · Answer 7

To prevent SQL Injection when the names of objects or columns are entered by the user, I'd recommend as well QUOTENAME() function. Of course, that doesn't remove the good practice of using parametrized queries. Combining both options, you should be safe. If anyone prove me wrong, we can all learn some more.

DECLARE @Table varchar(128) = 'sys.tables; '' SELECT TOP 100* FROM sys.columns'

DECLARE @sql nvarchar(4000)

SET @sql = 'SELECT * FROM ' + QUOTENAME(@Table)

PRINT @sql

EXEC sp_executesql @sql

Luis C.
General Disclaimer:
Are you seriously taking the advice and code from someone from the internet without testing it? Do you at least understand it? Or can it easily kill your server?

How to post data/code on a forum to get the best help: Option 1 / Option 2

gogniben SSC Veteran Points: 204 More actions · Answer 8

gogniben

SSC Veteran

Points: 204

July 29, 2016 at 7:40 am

#1892642

Thanks for another great article.

akljfhnlaflkj SSC Guru Points: 76202 More actions · Answer 9

Good article. We just try to avoid it altogether. We have some and are in the process of getting rid of it.