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How to Convert Between Date Formats in SQL Server using CAST()

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In SQL Server, you can use use the CONVERT() function to convert a date value from one date data type to another (or between any other data type for that matter). However, that’s not the only function in the T-SQL toolbox for converting between data types.

The CAST() function is part of the ANSI SQL standard, and it does most of the things CONVERT() does. So in many cases, you have the option of which of these functions you prefer to use.

Many database professionals prefer CAST() due to the fact that it’s part of the ANSI SQL standard, however, others prefer CONVERT() due to the extra functionality that T-SQL’s implementation offers (such as being able to provide a date style).

In any case, this article provides examples of converting between different date formats using CAST().

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How to Convert from One Date Format to Another in SQL Server using CONVERT()

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Sometimes when working with databases and other programming environments, you get a date value but it’s in the wrong format/data type. For example, if a date has been generated with an inbuilt date function, it might include both the date and the time, right down to the last nanosecond. And all you want is the day, month, and year, say like this: 2018-01-01.

If this happens while you’re using SQL Server, you can use the CONVERT() function to convert it to another data type. When you do this, the data type will determine the format it appears as.

This article provides examples of using the CONVERT() function in SQL Server to convert a date value to another (date) data type.

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How to Convert a String to a Date/Time in SQL Server using CAST()

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In SQL Server, you can use the CAST() function to convert an expression of one data type to another.  This function works almost the same as the CONVERT() function, except that the syntax is slightly different (and CAST() doesn’t accept the style argument).

So if you need to convert a string to a date/time value, you can use the CONVERT() function or the CAST() function.

And if you get an error while using those two functions, the PARSE() function might be just what you need.

This article contains examples using the CAST() function.

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6 Functions to Get the Day, Month, and Year from a Date in SQL Server

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Transact-SQL includes a bunch of functions that help us work with dates and times. One of the more common tasks when working with dates is to extract the different parts of the date. For example, sometimes we only want the year, or the month. Other times we might want the day of the week. Either way, there are plenty of ways to do this in SQL Server.

In particular, the following functions allow you to return the day, month, and year from a date in SQL Server.

These functions are explained below.

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How to Fix the “datediff function resulted in an overflow” Error in SQL Server

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This article provides a solution to a problem you may occasionally encounter while using the DATEDIFF() function in SQL Server.

If you encounter the following error:

The datediff function resulted in an overflow. The number of dateparts separating two date/time instances is too large. Try to use datediff with a less precise datepart.

It’s because the return value is too large. The DATEDIFF() function returns its result as an int data type. The reason you got this message is that the return value is too big for the int data type. Fortunately there’s an easy way to fix this.

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How to Replace NULL with Another Value in SQL Server – ISNULL()

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When querying a SQL Server database, there may be times where you don’t want null values to be returned in your result set. And there may be times where you do want them returned. But there may also be times where you do want them returned, but as a different value.

That’s what the ISNULL() function is for.

ISNULL() is a T-SQL function that allows you to replace NULL with a specified value of your choice.

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The SQL Server Equivalent to GROUP_CONCAT()

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Before SQL Server 2017 came along, there wasn’t a T-SQL equivalent of the MySQL GROUP_CONCAT() function. This function allows you to return a result set as a comma-separated list, as opposed to listing each row as a separate row (as with a normal result set).

Prior to SQL Server 2017, if you wanted to put your result into a comma separated list, you’d need to find a workaround, perhaps using a combination of STUFF() and FOR XML PATH().

However, T-SQL now has the STRING_AGG() function which is available from SQL Server 2017. This function does pretty much the same thing as MySQL’s GROUP_CONCAT() function (with some minor differences).

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How to Return Query Results as a Comma Separated List in SQL Server – STRING_AGG()

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Starting with SQL Server 2017, you can now make your query results appear as a list. This means you can have your result set appear as a comma-separated list, a space-separated list, or whatever separator you choose to use.

While it’s true that you could achieve this same effect prior to SQL Server 2017, it was a bit fiddly.

Transact-SQL now has the STRING_AGG() function, which concatenates the values of string expressions and places separator values between them. This works in much the same way to MySQL’s GROUP_CONCAT() function.

This article provides examples that demonstrate the T-SQL STRING_AGG() function.

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