Neoview SQL Reference Manual (R2.5)

Correlation Names
A correlation name is a name you can associate with a table reference that is a table, view,
materialized view, or subquery in a SELECT statement to:
• Distinguish a table or view from another table or view referred to in a statement
• Distinguish different uses of the same table
• Make the query shorter
A correlation name can be explicit or implicit.
Explicit Correlation Names
An explicit correlation name for a table reference is an SQL identifier associated with the table
reference in the FROM clause of a SELECT statement. The correlation name must be unique
within the FROM clause. For more information about the FROM clause, table references, and
correlation names, see “SELECT Statement” (page 164).
The syntax of a correlation name for the different forms of a table reference within a FROM clause
is the same:
{table | view | (query-expression)} [AS]correlation-name
A table or view is optionally followed by the AS keyword and the correlation name. A derived
table, resulting from the evaluation of a query expression, must be followed by the AS keyword
and the correlation name. An explicit correlation name is known only to the statement in which
you define it. You can use the same identifier as a correlation name in another statement.
Implicit Correlation Names
A table or view reference that has no explicit correlation name has an implicit correlation name.
The implicit correlation name is the table or view name qualified with the schema names.
You cannot use an implicit correlation name for a reference that has an explicit correlation name
within the statement.
Examples of Correlation Names
• This query refers to two tables (ORDERS and CUSTOMER) that contain columns named
CUSTNUM. In the WHERE clause, one column reference is qualified by an implicit correlation
name (ORDERS) and the other by an explicit correlation name (C):
SELECT ordernum, custname
FROM orders, customer c
WHERE orders.custnum = c.custnum
AND orders.custnum = 543;
238 SQL Language Elements