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.
If you’re using SQL Server, and you want to use T-SQL to change the size of an existing column, this article can help.
By “changing the size of an existing column”, I mean changing the data size. For example, say you have a varchar(255) but you want to increase its size to varchar(500). Here’s what you need to do in that case.
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.
This article demonstrates how to drop a column in a SQL Server database, when that column has an existing constraint (Hint: You need to drop the constraint first).
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.
When using MySQL, you can use the AVG() function to calculate the average value from a range of values.
For example, you can use this function to find out what the average city population is for a given country or state. Given a country will have many cities, each with different populations, you can find out what the average is between them. One city might have a population of say, 50,000 while another has a population of 500,000. The AVG() function will calculate the average for you.
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.
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.
If you’ve ever tried to concatenate a string with a number while using SQL Server, but received an error, this article should clear things up for you. There’s more than one way to perform concatenation using T-SQL in SQL Server, and if you’re concatenating different data types (like a string and a number) then you may receive an error, depending on how you do the concatenation.
The thing to remember when concatenating different data types is that they need to be converted into the same data type first. More specifically, when concatenating a string with a number, the number will need to be converted to a string before it can be concatenated with the string. Fortunately SQL Server/T-SQL makes this a breeze.
This article presents six ways to concatenate strings with numbers using T-SQL.
This article presents two methods for converting a decimal number to its hexadecimal equivalent in MySQL.
More specifically, I present two functions that enable you to do this conversion. The two functions are as follows:
HEX() functionCONV() functionBelow is an explanation of each function.