t-sql

How to Change a Column’s Data Type in SQL Server (T-SQL)

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When you create a database table, you specify all columns along with their data types. Once created, there’s not normally any intention of changing these data types. After all, whoever designed the schema would have put a lot of thought into what data type each and every column should accept.

However, we all know that things can change. Despite our best efforts at trying to foresee every possible scenario that may hit our database, sometimes that’s not enough.

So what do we do if we need to use Transact-SQL to change the data type of a column in SQL Server?

We use the ALTER TABLE statement to change it of course.

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How to Drop a Constraint in SQL Server (T-SQL)

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In SQL Server, a constraint defines rules that data in a database must comply with. For example, you could have a UNIQUE constraint applied to a column to ensure that any value inserted into that column is unique (i.e. no other row shares the same value).

If later on you need to remove that constraint, here’s how to do it using Transact-SQL.

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How to Add a New Column to an Existing Table in SQL Server (T-SQL)

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When you create a table in SQL Server using T-SQL, you specify all the columns for that table, along with their data types, any constraints, etc.

But what happens if one day you decide to add a new column to that table? How do you add the new column to the existing table without creating the table again? After all, dropping the table and starting again is usually not an option, as the table will already contain data, and you probably don’t want to have to backup all that data and re-insert it after dropping and creating the table.

The answer is: The ALTER TABLE statement.

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How to Add a DEFAULT Constraint to an Existing Column in SQL Server

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When using SQL Server, sometimes you need to modify an existing table. For the purposes of this article, say you want to add a DEFAULT constraint to an existing column.

To add a DEFAULT constraint to an existing column, use the ALTER TABLE statement and specify the column and the specific constraint that you want to apply.

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CONVERT() vs TRY_CONVERT in SQL Server: What’s the Difference?

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You might have noticed that T-SQL includes both a CONVERT() function and a TRY_CONVERT() function that you can use in SQL Server to perform conversions between data types. But if you’re scratching your head over what the difference is between these two functions, read on!

The difference between CONVERT() and TRY_CONVERT() is in the way they handle data types that can’t be converted. One throws an error, while the other returns null. The following examples demonstrate this.

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CAST() vs TRY_CAST() in SQL Server: What’s the Difference?

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When converting between data types in SQL Server, you will run into various functions that seemingly do the same thing. However, there are usually differences between these functions that might not be apparent at first glance. An example of this is the difference between the CAST() and TRY_CAST() functions.

This article demonstrates the difference between these functions when using SQL Server.

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How the SQL Server DIFFERENCE() Function Works

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This article aims to help you understand the DIFFERENCE() function, which is a T-SQL function available in SQL Server, Azure, etc.

The key to understanding the DIFFERENCE() function is to understand how Soundex works (or in the context of SQL Server, how the SOUNDEX() function works). This is because the DIFFERENCE() function returns the difference between the Soundex values between two strings.

A Soundex value is four characters long. If two words sound the same, they will share the same four character Soundex value. If they sound similar (but not the same), their Soundex values might share some characters but not all. For example, their Soundex values might have two characters the same and two that are different. If two words sound completely different, none of the characters in their respective Soundex values will be the same.

The DIFFERENCE() function returns a value that ranges from 0 through 4.  This value represents the number of characters in the Soundex values that are the same. 0 indicates weak or no similarity, and 4 indicates strong similarity or the same values.

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