SQL UNION Cheat Sheet with 10 Easy and Useful Tips

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.

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Using Alerts and Operators in SQL Server


With all the advancements in SQL Server and data, it feels great that such native SQL tools as Alerts and Operators are still available. They are the key SQL Server Agent features that are related to anything in SQL Server automation. 

Their roles are clear:

  • Alerts, when configured, let database administrators know when a specified event has occurred. 
  • An operator is an object defined within SQL Server that maps anyone or a group that can receive notifications when these events occur.

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T-SQL Regular expression: LIKE Operator and its use-cases

A Regular Expression (Regex) is a rule defining how characters can appear in an expression. In essence, it is a sequence of characters or text, which determines the search pattern.

The following are some of the use cases for regular expressions:

  1. To identify the data using combinations, such as credit or debit card numbers, email addresses, or telephone numbers.
  2. To find a specific text pattern or apply a filter to the text, numeric, or special character data.
  3. To parse the data in ETL by creating rules for inbound and outbound traffic and finding patterns in the code.

In SQL databases, selecting the values based on regular expressions defined in the WHERE condition is very useful.

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T-SQL SET Operators Part 2: INTERSECT and EXCEPT

In my previous article, I explained the basics of set operators, their types, and prerequisites for their use. I also talked about UNION and UNION ALL operators, their usage and differences.

In this article, we’re going to learn the following:

  1. EXCEPT and INTERSECT operators.
  2. Difference between INTERSECT and INNER JOIN.
  3. The detailed explanation of INTERSECT and EXCEPT with an example.

EXCEPT and INTERSECT operators were introduced in SQL Server 2005. Both are set operators used to combine the result sets generated by two queries and retrieve the desired output. Read More

Basic and Complex Uses of Not Equal Comparison Operator in T-SQL

This article is focused on the T-SQL Not Equal comparison operator (<>) and its uses in basic to slightly complicated SQL scripting tasks.

The article also highlights the importance of understanding the correct use of Not Equal comparative operator with expressions.

The Not Equal comparative operator is a very common operator used in T-SQL, however, it is important to understand how to use it effectively in different scenarios.

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In this article, we’ll look into the “APPLY” operator and its variations – CROSS APPLY and OUTER APPLY along with examples of how they can be used.

In particular, we will learn:

  • the difference between CROSS APPLY and the JOIN clause
  • how to join the output of SQL queries with table-evaluated functions
  • how to identify performance issues by querying dynamic management views and dynamic management functions.

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