The analysis results of each SELECT statement should have the same number of columns and the same field types to be merged.
If the SELECT result contains duplicate rows, UNION retains only one instance of each by default. To retain all, use UNION ALL.
Syntax Example
Merge two tables that have only one column. Among them, the first table has only one row with the value 13, and the second table has two rows with values 42 and 13. Merge the duplicate rows.
*|SELECT*FROM(VALUES13)
UNION
SELECT*FROM(VALUES42,13)
Return result:
Merge two tables that have only one column. Among them, the first table has only one row with the value 13, and the second table has two rows with values 42 and 13. Do not merge the duplicate rows.
