Having a hard time with SQL UNION? It happens if the results you combined put your SQL Server into a standstill. Or a report that’s been working before pops up a box with a red X icon. An “Operand type clash” error occurs pointing to a line with UNION. The “fire” starts. Sounds familiar?

Whether you’ve been using SQL UNION for a while or just start it out, a cheat sheet or a concise set of notes won’t hurt. This is what you are going to get today in this post. This list offers 10 useful tips for both newbies and veterans. Also, there will be examples and some advanced discussions.

But before we get into the first point, let’s clarify the terms.

UNION is one of the set operators in SQL that combines 2 or more result sets. It may come in handy when you need to combine names, monthly stats, and more from different sources. And whether you use SQL Server, MySQL, or Oracle, the purpose, behavior, and syntax will be very similar. But how does it work?

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