Openedge Data Management: SQL Reference - Product ...

Syntax
SELECT
In the above query, state is ambiguous because it can refer to either database column
pub.customer.state or the result of the substring scalar function in the SELECT list. The ANSI
standard requires that state refers unambiguously to the database column, therefore, the query
groups the result by the database column. The same principle holds true for ambiguous
references that appear in WHERE, ON, and HAVING clauses.
TOP clause
TOP n
Limits the rows returned by an OpenEdge SQL query at the statement level.
When the TOP clause is specified, the OpenEdge SQL server returns the maximum number
of rows specified in the clause. The maximum number allowed for the TOP clause is
2,147,483,647.
Example In the following example, the SELECT statement returns the names of the five customers with the
highest account balance:
SELECT TOP 5 FROM pub.customer
ORDER BY balance DESC;
The TOP clause is only allowed in a top-level SELECT statement. Therefore, the TOP clause cannot
be used in the following instances:
• As part of a subquery
• When derived tables are used in the query
• Within the CREATE TABLE, CREATE VIEW, UPDATE, and INSERT statements
• In queries used with set operators such as UNION, INTERSECT, and MINUS
In instances when the server performs aggregation on the result set (i.e., through an aggregate
function such as SUM or MAX, a GROUP BY clause, or the DISTINCT keyword) the TOP clause should
be interpreted as being applied last. When there is no aggregation in the SELECT statement and
the result set is also sorted, then SQL will optimize sorting in order to increase query
performance.
SELECT TOP is the functional equivalent of the Oracle ROWNUM functionality. Note that SELECT
TOP is defined simply in terms of a limit on the result set size, and the optimizer determines how
to use this limit for best data access. Thus, SELECT TOP does not have all the "procedural rules"
used to define the meaning of the Oracle ROWNUM phrase.
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