Function Calls
In addition to operators, SQLite supports both built-in and user-defined function calls. There
are two categories of function calls. Scalar functions are called with a specific set of parameters
and return a value, just like functions in almost any other expression
language. Scalar functions can be used in just about any context in any
SQLite expression. An example of a scalar function is abs(), which returns the absolute value of a
numeric parameter.
There are also aggregate functions, which are used to collapse or summarize
groups of rows. Aggregate functions can only be used in expressions that
define the result set or HAVING clause of
a SELECT statement. Aggregates are often
used in conjunction with GROUP BY
clauses. In essence, an aggregate function is called many times with
different input values, but returns only one value per dataset. An example
of an aggregate function is avg(), which
computes the average value for a sequence of numeric inputs.
The syntax for a function call looks like this:
As with many expression languages, a
function can be called by naming the function and providing a list of zero
or more comma-separated parameter expressions within a set of parentheses.
In some contexts, the special syntax of a single * character can also be used in place of a parameter list.
Like the result set definition of a SELECT statement, this has an implied meaning ...
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