## Compound Expressions

A compound expression specifies a combination of other expressions.

compound_expression::=

You can use any built-in function as an expression (Function Expressions). However, in a compound expression, some combinations of functions are inappropriate and are rejected. For example, the `LENGTH`

function is inappropriate within an aggregate function.

The `PRIOR`

operator is used in `CONNECT`

`BY`

clauses of hierarchical queries.

The `COLLATE`

operator determines the collation for an expression. This operator overrides the collation that the database would have derived for the expression using standard collation derivation rules.

Some valid compound expressions are:

('CLARK' || 'SMITH') LENGTH('MOOSE') * 57 SQRT(144) + 72 my_fun(TO_CHAR(sysdate,'DD-MMM-YY')) name COLLATE BINARY_CI