A conditional expression is an advanced form of the value
    expression that allows applications to return alternate
    information within an expression. See Value_Expressions for more
    information on the syntax. The following table describes the
    conditional expressions that are supported by Oracle Rdb.

    Table 3 Conditional Expressions

    Expression
    Name       Description

    ABS        ABS returns the absolute value of n.
    CASE       CASE alters the result of an expression. CASE can also
               generate or convert null values.
    COALESCE   COALESCE returns the first non-NULL value from a series
               of value expressions; otherwise, returns NULL.
    DECODE     Alternate form of the Case expression.
    GREATEST   GREATEST returns the greatest non-null value.
    LEAST      LEAST returns the least non-null value.
    NULLIF     NULLIF substitutes NULL when two value expressions are
               equal; otherwise, returns the first value.
    NVL        NVL returns the first non-NULL value from a series of
               value expressions; otherwise, returns NULL. NVL is a
               synonym for COALESCE.
    NVL2       If the first value expression to NVL2 is not NULL, then
               return the second value expression; otherwise return
               the third value expression.
    SIGN       SIGN returns the sign of the value