MIS 325 Lecture Notes - Lecture 13: Result Set
16 Apr 2018
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Document Summary
Subquery with no rows or only null values: always returns false. Subqueries that are executed once for each row that"s processed by the outer query. Similar to using a loop in a procedural programming language. Can be in select or where clause. Exists: tests whether or not the subquery returns a result set. Works like a view that"s temporarily created and stored in memory. Calculated values in result set must be assigned names. Most useful to further summarize results of a summary query. Can be restated using a join instead of a subquery. Subqueries are seldom coded because they"re slower and less readable than joins. Chapter 7: how to insert, update, and delete data. Only column definitions and data are copied. Definitions of primary keys, foreign keys, indexes, default values, etc. are not included in the new table. A group of sql statements that must all be executed successfully before they are saved to the database.
