Sql-Server

In previous posts, I looked at how to read data from a table. Now, we need to look at how we do calculations on the data in the table.

The most basic calculation we might do is to count the number of rows in the table. The first example above does that.

What about the asterisk?

But also notice that is has an asterisk in the query. Some people worry about the asterisk being in their queries as usually having an asterisk isn’t a good idea. In fact, some customers have automated systems for checking code, and the automated system might complain about the asterisk.

2021-02-15

Some time back, we added DateOfEasterSunday to our free SDU Tools for developers and DBAs. Given it was the Christian Easter Sunday, almost immediately, I got a request for the Greek Orthodox Easter. That date isn’t of course just the Greek one, so we’ve added a new function DateOfOrthodoxEaster.

It’s based on a concept from Antonios Chatzipavlis. Thanks !

It takes a single parameter:

@Year int - the year to find the date for

2021-02-12

In a previous post, I showed how to use CAST and CONVERT. What I didn’t mention before though, is what happens when the conversion will fail. If I try to convert the string ‘hello’ to an int, that just isn’t going to work. Of course, what does happen, is the statement returns an error.  Same thing happens if I try to convert the 30th February 2016 to a date. There aren’t 30 days in February. Again, an error will be returned.

2021-02-10

In our free SDU Tools for developers and DBAs, we have a lot of procedures and functions for checking system and database configuration details. One that we were asked for a function for, was the ability to check if the LockPagesInMemory (LPIM) setting was enabled, so we added that.

The function is called IsLockPagesInMemoryEnabled.

It takes no parameters, and returns a bit to indicate if the value is enabled or not.

2021-02-05

I was doing some consulting recently and reviewing a developer’s code. I was surprised to find extensive use of global temporary tables. Let me start by saying this: global temporary tables are almost never what you should be using.

When I asked why he’d used them, he told me that he wanted the temporary tables that he created in his procedure, to be available to other procedures that were run from within the procedure. So in PROC-A, he was running PROC-B and PROC-C. A temporary table was created in PROC-A and he wanted to be able to use it in PROC-B and PROC-C.

2021-02-04

Sometimes we need to determine whether a string is a date or whether it is a number.

In the first example above, I’m asking if the string ‘20190229’ is a valid date. You can see from the response (0) that it isn’t. That’s because even though it’s a valid date format, February in 2019 doesn’t have a 29th day. It’s not a leap year.

The value returned from the ISDATE function is a zero or a 1.  Curiously, the return value is of data type int. You’d think that a function that starts with Is and tests something would return a bit data type instead. But that’s just one of the curiosities of T-SQL.

2021-02-01

I’ve had a lot of good feedback about the options that we’ve provided in our free SDU Tools for developers and DBAs for formatting strings. Someone recently asked for a format with all capitals and dashes in between. I realised we didn’t have that, and we’ve added it. Generally, in the industry, this is referred to as Cobol Case.

So, we added a function CobolCase.

It takes one parameter:

@InputString - the string to be formatted

2021-01-29

We all use IN when writing queries:

SELECT ProductID, ProductName, Color, Size 
FROM dbo.Products 
WHERE Size IN ('370ml', '220ml');

A challenge comes up though, when you want to find pairs of values using IN. For example, if I have the following pairs of values:

Size        Color  370ml   Blue 370ml   Red 220ml   Blue

How do I find those when using IN?

Other databases do allow you to have pairs:

SELECT ProductID, ProductName, Color, Size
FROM dbo.Products 
WHERE (Size, Color) 
    IN (('370ml', 'Blue'), ('370ml', 'Red'), ('220ml', 'Blue'));

I wish T-SQL had that option but it doesn’t. It would be particularly useful when those values in the IN clause are coming from a sub-query.

2021-01-26

If you are using a string that was provided by another system, it might not be in the format that you were hoping it would be. So for example, if I have this string that says 2/29/2016, I know that’s a US date format, but if it was only 5/4/2016, there’s no way I could just easily tell that.

Conversion functions use your session settings to determine how to convert the values. When I’m converting strings to dates (and/or times), I certainly don’t want to change my settings so that I run with US configuration.

2021-01-25

I spend a lot of time doing data conversion work. It’s hard to imagine how much of that relates to working with dates and times. A requirement that I had recently was to find the nearest weekday to a given date i.e. find me the closest Thursday to a supplied date.

The NearestWeekday function in our free SDU Tools for developers and DBAs, does this.

It takes two parameters:

@TargetDate date - the date that we’re aiming for @DayOfWeek int - Sunday = 1, Monday = 2, Tuesday = 3, etc. (values from 1 to 7)

2021-01-22