Shulou(Shulou.com)06/01 Report--

Basic principle: each result set must have the same number of columns; the columns of each result set must be of compatible types.

SELECT FName FROM T_Employee UNION

SELECT FName FROM T_TempEmployee

one

SELECT FName FROM T_Employee

UNION ALL

SELECT FName FROM T_TempEmployee

Note: UNION merges two query result sets and merges completely duplicate rows into one. Union is inefficient because it needs to scan duplicate values, so if you are not sure you want to merge duplicate rows, use UNION ALL

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