UNION Operator

Use UNION operator to combine multiple query results. In other words, UNION can combine different rows into one table, those column in result table can have different data types(finally will be converted into same type, except NULL), but with the same column name.

SELECT [columns1]
FROM [table]
ORDER BY [column]

UNION

SELECT [columns2]
FROM 
[table1] JOIN [table2]
ON [condition]

• [columns2] must contain the same number of [columns2], or it will raise an error when executing the query.

• The names of result columns are specified by the very first query.

• If the a column in result table contains different types of data, those data will be converted into a same type, in most cases, will be converted into String.