Invoke a function that is bound to an operator
Functions that are bound to specific operators get invoked
automatically without explicit invocation. Suppose an equal() function
exists that takes two arguments of type1 and returns a Boolean.
If the equal operator (=) is used for comparisons between two columns, col_1 and col_2,
that are of type1, the equal() function
is invoked automatically. For example, the following query implicitly
invokes the appropriate equal() function to evaluate
the WHERE clause:
SELECT * FROM tab_1
WHERE col_1 = col_2The preceding query evaluates
as though it had been specified as follows:
SELECT * FROM tab_1
WHERE equal (col_1, col_2)