How to Use the CASE Statement in SQL

SQL as a scripting language is a valuable tool for data analysis. In case you are looking forward to an interview on SQL, make sure to sharpen your knowledge of how to use the case statement in SQL. Many interviewers go through this question; therefore, we would like to explore the best answers for you.

What is the Case Statement in SQL?

The ?case statement?in SQL is a method of operating the if/then logic. In other words, it expresses the functionality of an If?then?else statement. Here?is the basic syntax of the case statement:

CASE (expression)

When condition?1 Then result?1
When condition?2 Then result?2
When condition_n Then result_n
Else outcome

END

The SQL?case statement evaluates an array of conditions and returns one of the several possible outcome expressions.?We can break it down into two formats:

• The simple case expression which matches a single expression to a group of basic expressions to provide an outcome.
• The searched case expression that evaluates a group of Boolean functions to give the outcome.

SQL CASE Statement Arguments

The arguments used in the case statement include:

• Input expression: this is a valid expression employed in the simple case format.
• When?expression: it is a simple expression that the expression of input is usually compared to when the simple case format is employed. They must contain similar or implicitly converted data types.
• Then or result?expression: it is the expression received when the Boolean expression of input_expression equals to the when_expression returns true.
• Else or else?result?expression: it is the output expression when the operation evaluates to true. When the argument is omitted such that there is no comparison, the operation will result to null rather than true or false.
• When or Boolean expression: used in the searched case format and represents any valid Boolean expression.

Where is the SQL CASE Statement Used?

The SQL server case statement can be used in SQL Server 2014, 2012, 2008 R2, 2008 and 2005. You should note that the ELSE condition in the case statement is optional and can be done eradicated. The only difference would be that when it is omitted, and none of the arguments are satisfied as true, the outcome would be null.

The conditions listed within the argument in a case statement can be stringed. In other words, it can be employed to compare different conditions. However, the conditions will be operated on in the order in which they appear. When the first condition is true, the case statement may not proceed to the following conditions. An example of this is outlined below:

CASE

When x < y Then ?submit’
When c < d Then ?revise?

END

These two arguments are different. However, they are all computed by the case statement.

The case statement in SQL?is a powerful tool and when correctly used, it can evaluate two different fields or conditions. This article?will ensure that you are better placed at answering the question. Therefore, go through it well before the interview and also share your opinion or examples.