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This document covers the following topics:
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).
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+
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-
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*
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/
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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.
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A factor can consist of one of
the items listed in the above diagram and described in the text below.
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parameter |
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An atom can be either a
parameter
or a constant.
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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.
Note:
A table name in this context must not be qualified explicitly with
an authorization identifier. Use a correlation name instead if you need a
qualified table name.
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).
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COUNT
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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:
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 ...
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
Specifies a timestamp with time zone value:
AT
LOCAL or
AT TIME
ZONE
AT
LOCAL|
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function-invocation |
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{AT
LOCAL}
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AT TIME
ZONE|
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function-invocation |
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{AT
TIME ZONE}
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function-invocation |
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special-register
USER
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A reference to a
special-register returns a scalar
value.
| (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).