How are union operations denoted in SQL?

In SQL, union operations are denoted by the keyword "UNION." This operation combines the results of two or more SELECT statements into a single result set. The SELECT statements must have the same number of columns in the result sets with similar data types.

The correct understanding here is that you do not use commas, spaces, ampersands, or semicolons to denote union operations. Instead, you explicitly type "UNION" in your SQL query between the individual SELECT statements.

The use of a space, as mentioned in the provided choice, does not accurately represent how unions are performed in SQL. Spaces are used in SQL syntax generally for readability and do not impact the function or operation like a union.

For example, a valid SQL union operation looks something like this:

SELECT column1, column2

FROM table1

UNION

SELECT column1, column2

FROM table2;

In this structure, "UNION" is the critical term connecting the two SELECT statements. Users must also keep in mind that different variations such as "UNION ALL" exist, which include duplicates from the result sets, but fundamentally, unions are always expressed using the "UNION" keyword, making this the crucial