The UNION command is used to select related information from two tables, much like the JOIN command. However, when using the UNION command all selected columns need to be of the same data type. With
UNION
ALL
The UNION ALL command is equal to the UNION command, except that UNION ALL selects all values.
The difference
between UNION and UNION ALL is that UNION ALL will not eliminate
duplicate rows, instead it just pulls all rows from all the tables fitting your
query specifics and combines them into a table.
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