Minus (-)

The MINUS Operation (Set Difference)

The MINUS operation, written with the minus sign (−), answers a simple question: Which rows exist in the first table but not in the second? It is also called set difference. Figure 1.5 shows this as a Venn diagram — the crescent of one circle lying outside the other.

Using the same DANCE and MUSIC relations, suppose you want the list of students who are participating only in Music and not in Dance:

SELECT * FROM Music
MINUS
SELECT * FROM Dance;

The output — shown in Table 1.14 — gives the three students who are in the Music table but not in the Dance table: Mehak, Lavanya and Abhay. Notice that the table heading in the textbook reads "DANCE - MUSIC" — this is a minor labelling error in the original text; the operation correctly returns Music minus Dance.

How It Works

• The operation compares two tables (or result sets) that must have the same structure — same number of columns and compatible data types.
• It returns only those rows that appear in the first table and are absent from the second table.
• Duplicate rows are automatically removed from the result (just like in set theory).

Key Points to Remember

• MINUS is a set operation, not a join. It compares entire rows, not just key columns. …