----------  Scalar Subquery  ----------

<scalar subquery> specify a scalar value from a <query expression>.

According to ANSI, the degree of a <scalar subquery> should be 1, and
the cardinality is null or 1, if it is great than 1, an exception
condition is raised: "cardinality violation". For Empress error message,
it is "cardinality violation on scalar subquery"

Empress supports <scalar subquery> in SELECT, INSERT and UPDATE commands.
Please note <scalar subquery> in SELECT and INSERT commands is independent;
and in UPDATE command, it can be either independent or dependent.

For further information, enter:

        help insert;
        help select;
        help update;
