SQL SERVER – A Puzzle – Swap Value of Column Without Case Statement
- by pinaldave
For the last few weeks, I have been doing Friday Puzzles and I am really loving it. Yesterday I received a very interesting question by Navneet Chaurasia on Facebook Page. He was asked this question in one of the interview questions for job. Please read the original thread for a complete idea of the conversation. I am presenting the same question here.
Puzzle
Let us assume there is a single column in the table called Gender. The challenge is to write a single update statement which will flip or swap the value in the column. For example if the value in the gender column is ‘male’ swap it with ‘female’ and if the value is ‘female’ swap it with ‘male’.
Here is the quick setup script for the puzzle.
USE tempdb
GO
CREATE TABLE SimpleTable (ID INT, Gender VARCHAR(10))
GO
INSERT INTO SimpleTable (ID, Gender)
SELECT 1, 'female'
UNION ALL
SELECT 2, 'male'
UNION ALL
SELECT 3, 'male'
GO
SELECT *
FROM SimpleTable
GO
The above query will return following result set.
The puzzle was to write a single update column which will generate following result set.
There are multiple answers to this simple puzzle. Let me show you three different ways. I am assuming that the column will have either value ‘male’ or ‘female’ only.
Method 1: Using CASE Statement
I believe this is going to be the most popular solution as we are all familiar with CASE Statement.
UPDATE SimpleTable
SET Gender = CASE Gender WHEN 'male' THEN 'female' ELSE 'male' END
GO
SELECT *
FROM SimpleTable
GO
Method 2: Using REPLACE Function
I totally understand it is the not cleanest solution but it will for sure work in giving situation.
UPDATE SimpleTable
SET Gender = REPLACE(('fe'+Gender),'fefe','')
GO
SELECT *
FROM SimpleTable
GO
Method 3: Using IIF in SQL Server 2012
If you are using SQL Server 2012 you can use IIF and get the same effect as CASE statement.
UPDATE SimpleTable
SET Gender = IIF(Gender = 'male', 'female', 'male')
GO
SELECT *
FROM SimpleTable
GO
You can read my article series on SQL Server 2012 various functions over here.
SQL SERVER – Denali – Logical Function – IIF() – A Quick Introduction
SQL SERVER – Detecting Leap Year in T-SQL using SQL Server 2012 – IIF, EOMONTH and CONCAT Function
Let us clean up.
DROP TABLE SimpleTable
GO
Question to you:
I came up with three simple tricks where there is a single UPDATE statement which swaps the values in the column. Do you know any other simple trick? If yes, please post here in the comments. I will pick two random winners from all the valid answers. Winners will get 1) Print Copy of SQL Server Interview Questions and Answers 2) Free Learning Code for Online Video Courses
I will announce the winners on coming Monday.
Reference: Pinal Dave (http://blog.SQLAuthority.com)
Filed under: CodeProject, PostADay, SQL, SQL Authority, SQL Interview Questions and Answers, SQL Puzzle, SQL Query, SQL Server, SQL Tips and Tricks, SQLServer, T SQL, Technology
