Union queries are very useful in business operations, whether you are using SQL or Access. It allows you to combine the results of different Select statements together – basically combining results from separate sets of data. In a Union query, each Select statement is executed separately, and then their results are displayed one after the other. Unlike a Join query, a Union query does not require a relating field/data between the data sources.
But how can this be useful in your business operations?It is normal for a business to have many different data sources: stock orders, customers, employees, vendors, sales transactions, etc. There will be times that you need to get data that is scattered across these different data sources into one query.
Here are some examples where Union queries can be used to collate data for your business:
Creating Mailing lists – One of the most common examples of using Union queries is to get the contact information for Employees, Suppliers/Vendors, and Customers from different data sources. With Union queries, it is easy to get contact details, names, and other user-specific data for mailing lists or other data use (e.g. determining locations of suppliers and customers).
Stock/Inventory management – Incoming and outgoing stock/inventories are usually tracked separately using Purchase/Order and Sale/Dispatch tables. Using Union queries, it is possible to quickly bring the two data sources together to help determine the current stock levels.You can get data on dates, product names and other identifiers, and the amount of stock that either came in or were taken out.
Combining multiple instances of the same table – Sometimes, by accident or design, you’ll find that you have multiple tables where you should only have one. Someone may have accidentally copied data and worked on the copy or someone had to work offline and had to use a copy to update the main data source later. Union queries can be helpful in combining these multiple tables.
Collating data from different sources- An example where you have different data sources is if you have field agents or branch offices that are not connected or don’t have access to the main offices’ data. They would have to work on their own local data that they then send to the main office. These can be expense reports, sales orders, field reports, schedules, or other data that the main office will need to collate and keep track of using Union queries.
Merging data due to business changes – Another cause of having multiple tables is when your business acquires/ merges with another business. You will want to add their data to your existing data – which Union queries can facilitate.
While this is just a short list, it does give a general idea on the instances of when you will need to use Union queries. You may need to combine results from different data sources more often than you initially thought.
But why not just copy and paste the multiple data sources together, you may ask? That’s because the data sources may not be in the same table layout or arrangement of columns. One data source may have additional columns/information that the other data source does not have. In this case, you’ll have to manually filter or reorder the data – something that can take a lot of time if you have a large amount of data and data sources.
With Union queries, the Select statements allow you not only to reorder the arrangement of columns but specify which columns in the data sources are returned by the query. This convenience of combining data from different data sources is the main factor on why Union queries can make a difference in your business.
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