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

  • Greg Larsen

    SSC-Insane

    Points: 20585

    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

  • h.tobisch

    SSCommitted

    Points: 1661

    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

    SSCarpal Tunnel

    Points: 4898

    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: 1648

    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: 2845

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

  • Eirikur Eiriksson

    SSC Guru

    Points: 182336

    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: 182336

    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: 183517

    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

    Thanks for another great article.

  • akljfhnlaflkj

    SSC Guru

    Points: 76202

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

Viewing 10 posts - 1 through 10 (of 10 total)

You must be logged in to reply to this topic. Login to reply