SQL SUBQUERIES COUNTERPARTS IN TUTORIAL D
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Download SQL Tutorial. SQL uses the term subquery to refer to a table expression (commonly known as a query) that is contained within another table expression. Until 1992, as far as the international standard for SQL is concerned, subqueries were permitted only inside conditional expressions (i.e., truth-valued expressions), and conditional expressions were permitted only inside the WHERE clause, and the HAVING clause. Nowadays subqueries are permitted in the FROM and SELECT clauses too (and truth-valued expressions can appear in the SELECT clause, but we don't need to look at examples of those here).
Tutorial D has no restrictions on what type of expression is permitted where, apart from the usual rule that the type of an expression must be appropriate to the context in which it appears. (E.g., both operands of "=" must be of the same type, and both operands of JOIN must be of some relation type.)
Download SQL Tutorial
Tutorial D has no restrictions on what type of expression is permitted where, apart from the usual rule that the type of an expression must be appropriate to the context in which it appears. (E.g., both operands of "=" must be of the same type, and both operands of JOIN must be of some relation type.)
Download SQL Tutorial
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