How does MySQL execute a JOIN query statement?

5 months ago

1 minute

In MySQL, you can use the UNION keyword to perform a union query statement. Union query allows you to merge the results of multiple SELECT statements into one result set. Here is a simple example:

SELECT column1, column2 FROM table1
UNION
SELECT column1, column2 FROM table2;

In this example, data from column1 and column2 in table1 is first queried, followed by data from column1 and column2 in table2. Finally, the two result sets are combined into one.

You can use the UNION ALL keyword to include duplicate rows.

SELECT column1, column2 FROM table1
UNION ALL
SELECT column1, column2 FROM table2;

It is important to note that the difference between UNION and UNION ALL is that UNION removes duplicate rows, while UNION ALL retains all rows, including duplicates.