Handling set-based operations in SQL

StackOverflow https://stackoverflow.com/questions/19942553

Question

I'm trying to better understand set-based logic and simplify a piece of code I'm working on. Here's an example of what I am currently working with (it doesn't work currently for reasons that will quickly become apparent):

SELECT
    userid,
    rn = ROW_NUMBER() OVER (ORDER BY username) 
    FROM user 
    WHERE username like 'test%'

WHILE rn between 1 and 100
    <RUN SP USING INFORMATION>
WHILE rn between 101 and 200
    <RUN SP WITH DIFFERENT INFORMATION>

For the purposes of example, assume there are 200 rows that meet the criteria in the SELECT statement. Also assume that we can't make changes to the user table. My question is, without using a temp table and without (hopefully) using a WHILE loop, how else could I handle this?

Note that the SP referenced is a rather complex stored procedure that needs to use the information within that SELECT statement. I could handle this by using a temp table and going row by row, but I'm trying to understand other approaches to this where I could handle it in batches.

Was it helpful?

Solution 2

You can't call a stored procedure as part of another query, so it would be impossible to do what you're asking as a set-based operation without rewriting the stored procedures.

OTHER TIPS

Several years ago I wrote a SQL-based utility specifically to address needs like this. It is detailed in this article at another site here: http://www.sqlservercentral.com/scripts/Administration/69737/. (If you want, I can include it here as well, but it is fairly long)

Please note the following about it:

  1. It is written entirely in T-SQL, and
  2. It uses no Cursors or While loops whatsoever.

You would probably address your problem with this tool something like this:

EXECUTE OVER_SET '
    IF {rn} between 1 and 100
        <RUN SP USING INFORMATION>
    IF {rn} between 101 and 200
        <RUN SP WITH DIFFERENT INFORMATION>
    ',
@from = '
    (SELECT
            userid,
            rn = ROW_NUMBER() OVER (ORDER BY username) 
    FROM user 
    WHERE username like ''test%'') aa '
@subs1 = '{userid}=userid',
@subs2 = '{rn}=rn',
@quote = '"'        -- Allows you to use (") for quotes inside the 1st string
;

Since that is a sign-up site, I am posting the code below (long):

CREATE PROC 
  OVER_SET (
    @command AS NVARCHAR(MAX),       -- Template SQL command
    @from    AS NVARCHAR(MAX),       -- FROM..WHERE clause string
    @subs1   AS NVARCHAR(MAX) = N'', -- Substitution parameters, these are
    @subs2   AS NVARCHAR(MAX) = N'', -- of the form "<find>=<repl>" where:
    @subs3   AS NVARCHAR(MAX) = N'', -- <find> will be searched for in @command, and
                     -- <repl> will replace it, if it was found
                     -- (typically, <repl> should be a column name
                     -- returned by the FROM clause)
    @print   AS BIT = 1,             -- 0 = suppress PRINT of the SQL before executing
    @catch   AS VARCHAR(12) = 'continue',
                     -- TRY/CATCH option parameters. Choices are:
                     -- 'continue' on an error, print a message & continue
                     -- 'ignore' attempt to suppress all errors
                     -- 'fail' try to re-raise the error
                     -- 'none' no TRY/CATCH blocks
    @use_db  AS NVARCHAR(255) = N'', -- DB to switch to befor execution of the SQL text
    @quote   AS NVARCHAR(8)   = N''  -- search for this character & replace with (').
    )
AS
--
DECLARE @qt AS NVARCHAR(1), @cr AS NVARCHAR(1);
SELECT  @qt = N'''',        @cr = N'
';
DECLARE @find1  AS NVARCHAR(MAX), @prfx1  AS NVARCHAR(MAX), @sufx1 AS NVARCHAR(MAX)
DECLARE @find2  AS NVARCHAR(MAX), @prfx2  AS NVARCHAR(MAX), @sufx2 AS NVARCHAR(MAX)
DECLARE @find3  AS NVARCHAR(MAX), @prfx3  AS NVARCHAR(MAX), @sufx3 AS NVARCHAR(MAX)
DECLARE @prtst  AS NVARCHAR(MAX), @prfxC  AS NVARCHAR(MAX), @sufxC AS NVARCHAR(MAX)
DECLARE @newdb  AS NVARCHAR(MAX), @declr  AS NVARCHAR(MAX)
DECLARE @NewCmd AS NVARCHAR(MAX), @GenCmd AS NVARCHAR(MAX)
;
SELECT
 @find1 = CASE WHEN @subs1 = N'' THEN N'' ELSE LEFT(@subs1,CHARINDEX(N'=',@subs1)-1) END,
 @prfx1 = CASE WHEN @subs1 = N'' THEN N'' ELSE N'REPLACE(' END,
 @sufx1 = CASE WHEN @subs1 = N'' THEN N'' ELSE N',@find1,'+RIGHT(@subs1,LEN(@subs1)-CHARINDEX(N'=',@subs1))+N')' END,
 @find2 = CASE WHEN @subs2 = N'' THEN N'' ELSE LEFT(@subs2,CHARINDEX(N'=',@subs2)-1) END,
 @prfx2 = CASE WHEN @subs2 = N'' THEN N'' ELSE N'REPLACE(' END,
 @sufx2 = CASE WHEN @subs2 = N'' THEN N'' ELSE N',@find2,'+RIGHT(@subs2,LEN(@subs2)-CHARINDEX(N'=',@subs2))+N')' END,
 @find3 = CASE WHEN @subs3 = N'' THEN N'' ELSE LEFT(@subs3,CHARINDEX(N'=',@subs3)-1) END,
 @prfx3 = CASE WHEN @subs3 = N'' THEN N'' ELSE N'REPLACE(' END,
 @sufx3 = CASE WHEN @subs3 = N'' THEN N'' ELSE N',@find3,'+RIGHT(@subs3,LEN(@subs3)-CHARINDEX(N'=',@subs3))+N')' END,
 @newdb = CASE WHEN @use_db= N'' THEN N'' ELSE N'USE [' + @use_db + N'];' + @cr END,
 @declr = N'DECLARE @_Num AS INT, @_Lin AS INT, @_Err AS NVARCHAR(MAX), @_Msg AS NVARCHAR(MAX);'+@cr
;
;WITH
 [base] AS (SELECT cmd = @command),
 [quot] AS (SELECT cmd = CASE @quote WHEN N'' THEN cmd ELSE REPLACE(cmd, @quote, @qt) END FROM [base]),
 [dble] AS (SELECT cmd = N'N'+@qt+REPLACE(cmd, @qt, @qt+@qt)+@qt FROM [quot]),
 [prnt] AS (SELECT cmd = CASE @print WHEN 1 THEN N' PRINT '+cmd+';'+@cr ELSE N'' END
                       + N' EXEC('+cmd+N');' FROM [dble]),
 [ctch] AS (SELECT cmd = 
    CASE @catch WHEN N'none' THEN cmd 
    ELSE N'BEGIN TRY'+@cr+cmd+@cr+N'END TRY'+@cr+N'BEGIN CATCH'+@cr
    + N' SELECT @_Num=ERROR_NUMBER(), @_Lin=ERROR_LINE(), @_Err=ERROR_MESSAGE()'+@cr
    + CASE @catch
        WHEN N'continue' THEN 
                N' SELECT @_msg=''Continuing after Error(''+CAST(@_Num AS NVARCHAR)+'') at Line ''+CAST(@_Lin AS NVARCHAR)+'''
                         +@cr+' ''+@_Err;'+@cr
               +N' PRINT @_msg; '+@cr
               +N' PRINT '' ''; '+@cr
        WHEN N'ignore' THEN N' -- ignore = do nothing'+@cr
        WHEN N'fail' THEN
                N' SELECT @_msg=''Failing after Error(''+CAST(@_Num AS NVARCHAR)+'') at Line ''+CAST(@_Lin AS NVARCHAR)+'''
                         +@cr+' ''+@_Err;'+@cr
               +N' RAISERROR(@_Num, 16, 1);'+@cr
               +N' PRINT '' ''; '+@cr
        ELSE N' --BAD else branch, shouldnt get here' END
    + N'END CATCH;' END FROM [prnt])
SELECT 
    @NewCmd = @prfx1+@prfx2+@prfx3+ N'@command' +@sufx1+@sufx2+@sufx3,
    @command = cmd + @cr
FROM [ctch]
;
SELECT @GenCmd = '
DECLARE @sql AS NVARCHAR(MAX); SET @sql = '''+@newdb+ +@declr+ '''
;WITH 
  [-@from]  AS ( SELECT * FROM ' +@from+ ' )
, [-@subs]  AS ( SELECT [-NewCmd] = ' +@NewCmd+ ' FROM [-@from] )
, [-@print] AS ( SELECT [-NewCmd] = [-NewCmd] FROM [-@subs] )
SELECT 
  @sql = @sql + ''
'' + [-NewCmd]
FROM [-@subs]
;
EXEC sp_executesql @sql;
'
;
EXEC sp_executesql @GenCmd
, N'@command NVARCHAR(MAX), @from NVARCHAR(MAX), @find1 NVARCHAR(MAX), @find2 NVARCHAR(MAX), @find3 NVARCHAR(MAX)'
, @command, @from, @find1, @find2, @find3
;

Here are the post-comments which include some examples:

 Example Usages

1) INSERT..EXECute:
Demonstrates capturing the SELECT output from an EXECUTE OVER_SET that
searches every database in the SQL Server Instance for routines with
the work "cursor" in them.
--

CREATE TABLE #temp (DB sysname, [Schema] sysname, Routine sysname);
INSERT INTO #temp
  EXECUTE OVER_SET '
    SELECT ROUTINE_CATALOG, ROUTINE_SCHEMA, ROUTINE_NAME
      FROM [{db}].INFORMATION_SCHEMA.ROUTINES
      WHERE ROUTINE_DEFINITION like "%cursor%"',
    @from = 'sys.sysdatabases WHERE dbid > 4',
    @subs1 = '{db}=name',
    @quote = '"'
;
SELECT * from #temp;
DROP table #temp;

--
The @from argument returns the list of non-system databases in the server, 
and the @susbs1 argument "{db}=name" tells it to replace every instance 
of "{db}" in the command strings with the value of the [name] column (from 
sys.sysdatabases). Note also the @quote argument's value (") allows us to 
use a single quotation mark in the quoted command text instead of having
to use double apostrophes (ie, ' "%cursor%" ', instead of ' ''%cursor%'' '). 

--======

2) Nested Example:
Demonstrates, nesting OVER_SET execution to operate against the combination
of to different sets, the second dependent on the first. Specifically,
it searches every non-system database for every user that is a windows 
user or group, and then attempts to map them back to a server Login of
the same name.
--

EXECUTE OVER_SET '
   EXECUTE OVER_SET "
        ALTER USER [{name}] WITH LOGIN = [{name}]; 
        PRINT `USER {name} has been mapped to its Login.`;",
     @from   = "sys.database_principals
            WHERE ( type_desc = ""WINDOWS_GROUP"" OR type_desc = ""WINDOWS_USER"" )
            AND name NOT like ""%dbo%"" AND name NOT LIKE ""%#%"" ",
     @use_db = "{db}",
     @subs1  = "{name}=name",
     @catch  = "continue",
     @print  = 1,
     @quote  = "`";
     ',
  @from  = 'sys.sysdatabases
       WHERE dbid > 4',
  @subs1 = '{db}=name',
  @catch = 'continue',
  @print = 0,
  @quote = '"';

--
The outer OVER_SET uses the @from argument to return the list of all databases
which the @subs1 argument "{db}=name", uses to modify the inner OVER_SET
commands @use_db argument, cuasing the inner execution to USE [{db}} to each
database in turn. The inner execution's @from argument returns the list
of database users that are WINDOWS_* user or group, and the @subs1 ({name}=name)
cause the "{name}" token to be replaced with the value of the [name] column
from the database_principals table.

Note that two different @quote characters are used ( ("), then (`) ), removing
the need for double or even quadruple apostrophes in the inner command text.
(also note, that the @from argument text does not benefit from this, and can
only use the outer command quote (") becuase it is part of the outer command
text argument.

Is it possible to use UDFs instad of SP? In that case you can include the UDF with parameters from the SELECT statement in one go. Obviously UDFs have limitations but I guess it depends on the complexity of your SP.

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