+ -

factor (scalar-expression)

scalar-expression scalar-operator scalar-expression

This document covers the following topics:

• Scalar Expression

• Scalar Operator

• Factor

• Row Value Expression

---

Scalar Expression

A scalar-expression consists of a factor or other scalar expressions including scalar operators.

Concerning reference priority, scalar expressions behave as follows:

• When a non-qualified variable name is specified in a scalar expression, the first approach is to resolve the variable name as column name of the referenced table.

• If no column with the specified name is available in the referenced table, Natural tries to resolve this variable as a Natural user-defined variable (host variable).

Scalar Operator

	+
	-
	*
	/

A scalar-operator can be any of the operators listed above. The minus (-) and slash (/) operators must be separated by at least one blank from preceding operators.

Factor

atom column-reference aggregate-function special-register

A factor can consist of one of the items listed in the above diagram and described in the text below.

Atom

parameter constant

 An atom can be either a parameter or a constant.

Column Reference

table-name. correlation-name.

column-name

A column-reference is a column name optionally qualified by either a table-name or a correlation-name (see also the section Basic Syntactical Items). Qualified names are often clearer than unqualified names and sometimes they are essential.

If a column is referenced by a table-name or correlation-name, it must be contained in the corresponding table. If neither a table-name nor a correlation-name is specified, the respective column must be in one of the tables specified in the FROM clause (see Table Expression).

Aggregate Function

	COUNT				(*) (DISTINCT column-reference)
		AVG MAX MIN SUM			(DISTINCT column-reference) ([ALL] scalar-expression)

SQL provides a number of special functions to enhance its basic retrieval power. The so-called SQL aggregate functions currently available and supported by Natural are:

AVG	gives the average of the values in a column
COUNT	gives the number of values in a column
MAX	gives the highest value in a column
MIN	gives the lowest value in a column
SUM	gives the sum of the values in a column

Apart from COUNT(*), each of these functions operates on the collection of scalar values in an argument (that is, a single column or a scalar-expression) and produces a scalar value as its result.

Example:

DEFINE DATA LOCAL 
1 AVGAGE   (I2) 
END-DEFINE 
... 
SELECT AVG (AGE) 
  INTO AVGAGE 
  FROM SQL-PERSONNEL 
  ...

DISTINCT

In general, the argument can optionally be preceded by the keyword DISTINCT to eliminate redundant duplicate values before the function is applied.

If DISTINCT is specified, the argument must be the name of a single column; if DISTINCT is omitted, the argument can consist of a general scalar-expression.

DISTINCT is not allowed with the special function COUNT(*), which is provided to count all rows without eliminating any duplicates.

Time-Zone-Specific Expression

time-zone-specific-expression

Specifies a timestamp with time zone value: AT LOCAL or AT TIME ZONE

AT LOCAL

function-invocation (expression) constant column-name variable special-register scalar-fullselect case-expression cast-specification

{AT LOCAL}

AT TIME ZONE

function-invocation (expression) constant column-name variable special-register scalar-fullselect case-expression cast-specification

{AT TIME ZONE}

function-invocation (expression) constant column-name variable special-register scalar-fullselect case-expression cast-specification

Special Register

special-register

USER

A reference to a special-register returns a scalar value.

Row Value Expression

(scalar-expression,...)

A row-value-expression returns a single row that consists of one or more column values. The values can be specified as a list of expressions. The number of columns that are returned by the row-value-expression is equal to the number of expressions. row-value-expression can be used as an operand of several predicates (quantified, DISTINCT, comparison, and IN).