How Can I Combine Data from Multiple Tables Using SQL's UNION Operator?

Combining Tables for a Consolidated Output

When working with multiple data tables, combining them to produce a single, cohesive output can be a common task. To achieve this, understanding the data structure and query operations becomes crucial.

Imagine having two tables: KnownHours and UnknownHours. The goal is to merge these tables, disregarding the Month column, to obtain a comprehensive view of hours associated with various charge numbers and category IDs.

To accomplish this, the UNION operator serves as a powerful tool. It allows us to combine the results of multiple queries, essentially appending them together. The syntax for UNION in SQL is as follows:

In our case, we need to group the hours for each ChargeNum/Category combination. We can modify our UNION query as below:

The UNION ALL keyword differs slightly from UNION in that it makes no attempt to remove duplicate rows. This ensures that all rows from both queries are included in the final result.

By utilizing the UNION ALL operation, we can effectively combine the results from KnownHours and UnknownHours, creating a comprehensive table with the desired output:

Understanding the UNION operator empowers you to merge data from multiple sources, providing a powerful means to construct tailored and comprehensive outputs for your data analysis needs.

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