Category: Syntax

Dave Bland shows how you can build a dynamic pivot to see performance counter data over a stretch of time:

The next step is to write the code to capture the counter values and insert the data it the temporary table created above.  Because we need to capture the values over a period of time, the WAITFOR DELAY is used.  In this case the delay is 10 seconds, although you can change this to suit your needs. Of course, don’t forget to increment the counter variable. You will need to determine what counters you would like to capture.  Notice in the WHERE clause, we are looking for an instance_name of ” or ‘_total’.  This will allow the code to only capture one row for each counter.  The number 10 is the number of times we want to capture the counter values.  If you want to capture the data more frequently, simpley modify the number of seconds in the WAITFOR DELAY.  Here is link to my post in this topic, WAITFOR.

Dynamic pivoting in SQL is unnecessarily difficult, especially compared to languages like R.

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Jeffry Schwartz compares the performance of STRING_AGG in SQL Server 2017 versus the tried and true method of FOR XML PATH for string concatenation:

Two different T-SQL methods were used for testing.  The FOR XML PATH solution incorporates the reverse and stuff functions along with FOR XML PATH.  The String_agg solution is much simpler, but is only available on SQL Server 2017 currently.

The FOR XML PATH method has been documented thoroughly over the years in many articles, so these explanations will not be repeated here.  However, two points are worth mentioning.  The first one is that the @strSeparator (in this case ‘ or  ’) string will reside at the end of the constructed string (in this case @strFilter).  Since the last occurrence of @strSeparator must be removed to prevent a syntax error, characters must be dropped from the end of the string.  Although it may seem obvious that four characters (the length of @strSeparator) should be removed, actually only three need be removed because the end of the constructed string is “r” not “ “.  Therefore, the length argument of the left function specification is the length of @strFilter minus three.

I like STRING_AGG a lot, primarily because I can remember it and I can explain it to people relatively new to SQL Server. Read on to see how they both compare in terms of performance.

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Solomon Rutzky strives to solve the question, “What is the UNCOMPRESS function anyhow?”:

With no clear indications of what the UNCOMPRESS function does, we can at least pass in some simple values to see what comes back, and see if we can make sense of the output. For the following tests, please keep in mind that “8-bit” refers to the VARCHAR, CHAR, and TEXT (deprecated) datatypes. And, “16-bit” refers to the NVARCHAR, NCHAR, NTEXT (deprecated),and XML datatypes.

Read on as Solomon figures out what it does and how non-useful it is for anybody nowadays.

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Bert Wagner explains some of the trickiness of COUNT and NULL values in SQL Server:

One thing I see fairly often (and am occasionally guilty of myself) is using COUNT(DISTINCT) and DISTINCT interchangeably to get an idea of the number of unique values in a column.

While they will sometimes give you the same results, depending on the data the two methods may not always be interchangeable.

Click through for examples.

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Jen Stirrup explains why ISNUMERIC isn’t all that great:

I noted that one of the columns failed to convert VARCHAR to DECIMAL.

The error message is below, and it’s usually fairly easy to sort:
Error converting data type varchar to numeric

Normally, I’d use ISNUMERIC to identify the rows that fail to have a value in that column that could be converted to a number. Then, I could identify the value, and then I could replace or exclude it, as required.

However, on this occasion, using ISNUMERIC failed to identify any columns as being non-numeric. 

Click through to see why Jen got this result.

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