Example #2Īllot a grade to each student based on marks obtained by him/her in a subject. If it is TRUE then it returns ‘PASSED’ otherwise moves to the ELSE part of the statement and returns ‘FAILED’. SELECT student_id, first_name, last_name, subject, marks,Įxplanation: In the above example, the CASE statement checks the WHEN part, i.e if marks > 250 are TRUE. Let us discuss some examples to understand better: Example #1Īssuming that one should get at least 250 out of 500 marks to pass a subject, based on the marks obtained by a student in a particular subject, mention if he has passed or failed the subject. The data in the ‘students’ table after insertion looks something like this: Let’s insert some values in the table to populate the dataset using the INSERT statements. The ‘students’ table can be created in the following manner. The table will contain student details such as their student id, first name, last name, marks, subject, etc. To illustrate the functions and applications of the CASE statement in SQL, let’s create an imaginary ‘students’ table. Here are a few examples to illustrate the syntax and functions of CASE statements in SQL. Out of the above-mentioned parameters, all parameters except ELSE are compulsory.
We can provide an alias to the CASE using AS.
CASE: It is an essential keyword that is always used to mark the beginning of a CASE statement.Second, if you are careful, you can do some odd logic tasks when you understand exactly how something works. First, it’s really helpful when debugging to understand what’s actually happening and why you might be getting an error. So why do we care about any of this? Two reasons.
This will return (ignoring the fact that without an ORDER BY you have no guarantee of the order) two rows of data and then an error. So for example: SELECT CASE WHEN Col1/Col2 > 2 THEN 'More than 2' Now, I should point out that if you have this in a SELECT statement then the CASE will potentially be evaluated multiple times and can run you into an error even after you’ve gotten some data. Also, it looks like the boolean expressions aren’t checked by the parser when the query is checked. So the CASE expression stops evaluating after the first positive result.
SQL SERVER CASE HOW TO
I had a number of different thoughts on how to prove this but my first, and simplest option ended up doing the trick. So will a CASE expression short circuit? Let’s find out! Short Circuit: This means that if one of the boolean expressions evaluates to true then it doesn’t bother evaluating the rest of them.Ī command short-circuiting is somewhat language and command dependent. Really you can replace any value with a case expression in pretty much any command. Heck, you can even use it in the ORDER BY clause. Since this is inline you can’t just run this on its own, but you can put it in the field list, WHERE clause, HAVING clause, etc. This is going to be similar to a SWITCH in other languages. CASE Expression: This is basically an inline IF.