SQL Bible [Electronic resources] نسخه متنی

Assignment Operator

The assignment operator is one of the most
intuitive to use. It assigns a value to a variable. The only confusion in using
this operator could stem from its overloading. All RDBMS overload this operator
with an additional function — comparison — in the SQL.

The equals operator (=) is used as an assignment in the following SQL query
that updates the price (PROD_PRICE_N) column in
the
PRODUCT table, raising the existing prices
by 2 percent:

UPDATE product SET prod_price_n
= prod_price_n * 1.02 (10 row(s) affected)

And the same operator would be used for
comparing values when used, for example, in the
WHERE clause of an SQL statement:

UPDATE product SET prod_price_n
= prod_price_n * 1.02 WHERE prod_id_n = 1880 (1 row(s)
affected)

This statement assigns a 2 percent
increase to a product whose ID is 1880; in the same query, the equals operator
(=) is used in its assignment and comparison
capacity at the same time.