Generally speaking, the SQL queries that I write return unformatted data and I leave it to the presentation layer, a web page or a windows app, to format the data as required. Other people that I work with, including my boss, will insist that it is more efficient to have the database do it. I’m not sure that I buy that and believe that even if there was a measurable performance gain by having the database do it, that there are more compelling reasons to generally avoid this.
For example, I will place my queries in a Data Access layer with the intent of potentially reusing the queries whenever possible. Given this, I ascertain that the queries are more likely to be able to be reused if the data remains in their native type rather than converting the data to a string and applying formatting functions on them, for example, formatting a date column to a DD-MMM-YYYY format for display. Sure, if the SQL was returning the dates as formatted strings, you could reverse the process to revert the value back to a date data type, but this seems awkward, for lack of a better word. Furtehrmore, when it comes to formatting other data, for example, a machine serial number made up of a prefix, base and suffix with separating dashes and leading zeros removed in each sub field, you risk the possibility that you may not be able to correctly revert back to the original serial number when going in the other direction. Maybe this is a bad example, but I hope you see the direction I am going with this…
To take things a step further, I see people write VERY complex SQLs because they are essentially writing what I would call presentation logic into a SQL instead of returning simple data and then applying this presentation logic in the presentation layer. In my mind, this results in very complex, difficult to maintain and more brittle SQL that is less adaptable to change.
Take the following real-life example of what I found in our system and tell me what you think. The rational I was given for this approach was that this made the web app very simple to render the page as it used the following 1-line snippet of classic ADO logic in a Classic ASP web app to process the rows returned:
oRS.GetString ( , , "</td>" & vbCrLf & "<td style=""font-size:x-small"" nowrap>" ,"</td>" & vbCrLf & "</tr>" & vbCrLf & "<tr>" & vbCrLf & _
"<td style=""font-size:x-small"" nowrap>" ," " ) & "</td>" & vbCrLf & "</tr>" & vbCrLf & _
Here’s the SQL itself. While I appreciate the author’s ability to write a complex SQL, I feel like this is a maintenance nightmare. Am I nuts? The SQL is returning a list of programs that are current running against our database and the status of each:
Because the SQL did not display with CR/LFs when I pasted here, I decided to put the SQL on an otherwise empty personal Google site. Please feel free to comment. Thanks.
By the way-This SQL was actually constructed using VB Script nested WITHIN a classic ASP page, not calling a stored procedure, so you have the additional complexity of embedded concatentations and quoted markup, if you know what I mean, not to mention lack of formatting. The first thing I did when I was asked to help to debug the SQL was to add a debug.print of the SQL output and throw it through a SQL formatter that I just found. Some of the formatting was lost in pasting at the following link:
Edit(Andomar): copied inline: (external link removed, thanks-Chad)
SELECT
Substring(Datename("dw",start_datetime),1,3)
+ ', '
+ Cast(start_datetime AS VARCHAR) "Start Time (UTC/GMT)"
,program_name "Program Name"
,run_sequence "Run Sequence"
,CASE
WHEN batchno = 0
THEN Char(160)
WHEN batchno = NULL
THEN Char(160)
ELSE Cast(batchno AS VARCHAR)
END "Batch #" /* ,Replace(Replace(detail_log ,'K:\' ,'file://servernamehere/DiskVolK/') ,'\' ,'/') "log"*/ /* */
,Cast('<a href="GOIS_ViewLog.asp?Program_Name=' AS VARCHAR(99))
+ Cast(program_name AS VARCHAR)
+ Cast('&Run_Sequence=' AS VARCHAR)
+ Cast(run_sequence AS VARCHAR)
+ Cast('&Page=1' AS VARCHAR)
+ ''
+ Cast('">'
+ CASE
WHEN end_datetime >= start_datetime
THEN CASE
WHEN end_datetime <> 'Jan 1 1900 2:00 PM'
THEN CASE
WHEN (success_code = 10
OR success_code = 0)
AND exit_code = 10
THEN CASE
WHEN errorcount = 0
THEN 'Completed Successfully'
ELSE 'Completed with Errors'
END
WHEN success_code = 100
AND exit_code = 10
THEN 'Completed with Errors'
ELSE CASE
WHEN program_name <> 'FileDepCheck'
THEN 'Failed'
ELSE 'File not found'
END
END
ELSE CASE
WHEN success_code = 10
AND exit_code = 0
THEN 'Failed; Entries for Input File Missing'
ELSE 'Aborted'
END
END
ELSE CASE
WHEN ((Cast(Datediff(mi,start_datetime,Getdate()) AS INT) <= 240)
OR ((SELECT
Count(* )
FROM
MASTER.dbo.sysprocesses a(nolock)
INNER JOIN gcsdwdb.dbo.update_log b(nolock)
ON a.program_name = b.program_name
WHERE a.program_name = update_log.program_name
AND (Abs(Datediff(n,b.start_datetime,a.login_time))) < 1) > 0))
THEN 'Processing...'
ELSE 'Aborted without end date'
END
END
+ '</a>' AS VARCHAR) "Status / Log"
,Cast('<a href="' AS VARCHAR)
+ Replace(Replace(detail_log,'K:\','file://servernamehere/DiskVolK/'),
'\','/')
+ Cast('" title="Click to view Detail log text file"' AS VARCHAR(99))
+ Cast('style="font-family:comic sans ms; font-size:12; color:blue"><img src="images\DetailLog.bmp" border="0"></a>' AS VARCHAR(999))
+ Char(160)
+ Cast('<a href="' AS VARCHAR)
+ Replace(Replace(summary_log,'K:\','file://servernamehere/DiskVolK/'),
'\','/')
+ Cast('" title="Click to view Summary log text file"' AS VARCHAR(99))
+ Cast('style="font-family:comic sans ms; font-size:12; color:blue"><img src="images\SummaryLog.bmp" border="0"></a>' AS VARCHAR(999)) "Text Logs"
,errorcount "Error Count"
,warningcount "Warning Count"
,(totmsgcount
- errorcount
- warningcount) "Information Message Count"
,CASE
WHEN end_datetime > start_datetime
THEN CASE
WHEN Cast(Datepart("hh",(end_datetime
- start_datetime)) AS INT) > 0
THEN Cast(Datepart("hh",(end_datetime
- start_datetime)) AS VARCHAR)
+ ' hr '
ELSE ' '
END
+ CASE
WHEN Cast(Datepart("mi",(end_datetime
- start_datetime)) AS INT) > 0
THEN Cast(Datepart("mi",(end_datetime
- start_datetime)) AS VARCHAR)
+ ' min '
ELSE ' '
END
+ CASE
WHEN Cast(Datepart("ss",(end_datetime
- start_datetime)) AS INT) > 0
THEN Cast(Datepart("ss",(end_datetime
- start_datetime)) AS VARCHAR)
+ ' sec '
ELSE ' '
END
ELSE CASE
WHEN end_datetime = start_datetime
THEN '< 1 sec'
ELSE CASE
WHEN ((Cast(Datediff(mi,start_datetime,Getdate()) AS INT) <= 240)
OR ((SELECT
Count(* )
FROM
MASTER.dbo.sysprocesses a(nolock)
INNER JOIN gcsdwdb.dbo.update_log b(nolock)
ON a.program_name = b.program_name
WHERE a.program_name = update_log.program_name
AND (Abs(Datediff(n,b.start_datetime,a.login_time))) < 1) > 0))
THEN 'Running '
+ Cast(Datediff(mi,start_datetime,Getdate()) AS VARCHAR)
+ ' min'
ELSE ' '
END
END
END "Elapsed Time" /* ,end_datetime "End Time (UTC/GMT)" ,datepart("hh" ,
(end_datetime - start_datetime)) "Hr" ,datepart("mi" ,(end_datetime - start_datetime)) "Mins" ,datepart("ss" ,(end_datetime - start_datetime)) "Sec" ,datepart("ms" ,(end_datetime - start_datetime)) "mSecs" ,datepart("dw" ,start_datetime) "dp" ,case when datepart("dw" ,start_datetime) = 6 then ' Fri' when datepart("dw" ,start_datetime) = 5 then ' Thu' else '1' end */
,totalrows "Total Rows"
,inserted "Rows Inserted"
,updated "Rows Updated" /* ,success_code "succ" ,exit_code "exit" */
FROM
update_log
WHERE start_datetime >= '5/29/2009 16:15'
ORDER BY start_datetime DESC
The answer is obviously “just retrieve output”. Formatting on the SQL server has the following problems:
I’m sure there are many more.