Outer reference in SELECT clause of subquery

Oracle permits the SELECT clause of a subquery to reference a column which is an outer reference (ie correlated). This is illegal according to the 1989 SQL standard 5.24: Let R denote the result of the <table expression>. Each <column specification> in the <value expression> shall unambiguously reference a column of R).

For (a stupid) example:

        SELECT * FROM EMPS T WHERE AGE IN (SELECT T.AGE FROM EMPS); Has anyone used this non-standard feature in real life?

More to the point, why did the standard want to ban it? It is stupid to select an outer reference on its own because it is a constant during the evaluation of the subquery, but it is conceivably useful in a value expression.

• Roger

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* Roger MacNicol, Snr. Software Engineer

* VMark Software, Inc., 30 Speen Street, Framingham, MA 01701-1800


* email: uvmark%roger_at_merk.com