May 2020
Beginner
564 pages
14h 9m
English
Content preview from Learn SQL Database Programming
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Understanding what a UNION join is and learning how to use it in a SQL query
UNION allows you to combine two or more result sets into a single result set. There are a few rules that need to be followed to avoid errors, listed as follows:
- The number of columns in the SELECT statements must be the same.
- The order of the columns in the SELECT statements must be the same.
- The data types of the columns must be the same or of a compatible type.
- The ORDERBY clause can only be used on the final SELECT statement.
There are also a couple of things to keep in mind when reviewing your results, as follows:
- The names of the final columns are generated from the column names you use in the first SELECT statement.
- GROUP BY and HAVING clauses can only ...
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