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).
Category: DBMS
Database Management Systems
How to Add a DEFAULT Constraint to an Existing Column in SQL Server
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.
AVG() – Calculate the Average Value of a Column in MySQL
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.
CONVERT() vs TRY_CONVERT in SQL Server: What’s the Difference?
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.
CAST() vs TRY_CAST() in SQL Server: What’s the Difference?
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.
6 Ways to Concatenate a String and a Number in 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.
2 Ways to Convert between Decimal and Hexadecimal in MySQL
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:
- The
HEX()function - The
CONV()function
Below is an explanation of each function.
How to Convert a String to Hexadecimal in MySQL – HEX()
In MySQL, you can convert a string to its hexadecimal representation by using the HEX() function.
The HEX() function works on both strings and numbers, however, its handling of each of these is slightly different. When used to convert a number, it returns a hexadecimal string representation of the number treated as a longlong (BIGINT) number. But when converting a string, it returns a hexadecimal string representation of the string where each byte of each character is converted to two hexadecimal digits.
3 Ways to “Unhex” a String in MySQL
MySQL includes various functions that can assist you when working with hexadecimal values. One of the most obvious functions is the HEX() function, which enables you to convert a string into its hexadecimal equivalent.
However, there may be times where you want to convert a hexadecimal string back to a more readable string. That’s what this article is about.
Here are three ways to “unhex” a string in MySQL:
- The
UNHEX()function - The
Xhexadecimal notation - The
0xnotation
Below are examples of each of these methods.
How to “Unhex” a Number in MySQL
In MySQL, you can unhex a string using the UNHEX() function. But you can’t unhex a number with that function.
To unhex a number in MySQL, use the CONV() function instead.
The CONV() function allows you to convert numeric values between different numbering systems. For example, you can convert between say decimal and binary, octal to decimal, or, more relevant to this article, between hexadecimal and decimal.