How to query data from many tables using union in mysql?

by scotty_walker , in category: MySQL , 2 months ago

How to query data from many tables using union in mysql?

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1 answer

by wilmer.lemke , 2 months ago

@scotty_walker 

To query data from multiple tables using Union in MySQL, follow these steps:

  1. Start by writing the select statement for each table separately.
  2. Use the “UNION” keyword to combine the results of multiple select statements into a single result set.
  3. Make sure that the number of columns and their datatypes in each select statement are the same.
  4. If required, use the "ORDER BY" clause to sort the results. The order of the columns in the ORDER BY clause should match the order in the select statement.
  5. Run the query to retrieve the combined results.


Here's an example to demonstrate the process:

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SELECT column1, column2 FROM table1
UNION
SELECT column1, column2 FROM table2
UNION
SELECT column1, column2 FROM table3
ORDER BY column1;


In the above example, the columns "column1" and "column2" are selected from three different tables: table1, table2, and table3. The UNION keyword combines the results of all three select statements into a single result set. Additionally, the results are sorted by "column1" using the ORDER BY clause.