How to Use SQL CASE for Conditional Logic in Your SQL Queries

SQL CASE provides the author of the query with the ability to perform conditional logic in their SQL queries for SELECT, INSERT, UPDATE, DELETE. It is also possible to use it with SET, IN, HAVING, ORDER BY and WHERE. It comes in two formats: simple case search case Simple SQL CASE The simple CASE expression compares an expression to […]

Using ISNULL in SQL Server to Replace NULL Values

There are different ways to handle NULL’s and I wrote about one such way in my last post. In this post, we look at SQL ISNULL() and specifically at the SQL Server version. MySQL does have this function but it behaves a little differently as it returns a boolean value. Let’s look at the syntax ISNULL(check_expression, […]

Using SQL COALESCE to Find the First Non-NULL Value

You are looking to find a way to find the first non-null value from a list of fields. In this post, we look at SQL COALESCE – a wonderfully useful tool that helps to solve that problem. To help demonstrate this, we will talk about a hypothetical scenario where a number of customer leads have been added to a […]

T-SQL – How to Select Top N Rows for Each Group Using ROW_NUMBER()

I’ve recently been working on a data migration project and have found myself utilizing the ROW_NUMBER() function in SQL Server a lot. This function has been around since SQL Server 2005 and at its core, provides a way to provide sequential numbering for rows returned by a query. One of the requirements for an export process was […]

Data Management – Finding, Removing Duplicate Rows Using SQL and Some Prevention Tips

Duplicate data is a common problem and in my experience comes in two main flavours; exact duplicate data and similar data. Exact duplicate data is when a data source contains the same values across all fields in the record. Similar data is when some of the fields match and to the naked eye can be classed […]