Advanced SQL Database Programmers Handbook

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CREATE VIEW View1 AS SELECT MAX(column1) FROM Table1) then the similar query -- SELECT MAX(column1) FROM Table1 -- can just select from the view, even though the SELECT doesn't ask for the view. A DBMS might sometimes fail to realize that the view is usable, though, so occasionally you'll have to check what your DBMS's "explain" facility says. With Oracle you'll then have to use a hint, as in this example: SELECT/*+ rewrite(max_salary) */ max(salary) FROM Employees WHERE position = 'Programmer' Permanent materialized views are best for groupings, because for non-grouped calculations (such as one column multiplied by another) you'll usually find that the DBMS has a feature for "indexing computed columns" (or "indexing generated columns") which is more efficient.

The is probably reasonable, but it was not in the specifications. Another thing the specification did not tell us is what happens when a document has all the search words and some extras? Do we look only for an exact match, or can a document have more keywords? Fortunately, the operation of picking the documents that contain all the search words is known as Relational Division. It was one of the original operators that Ted Codd proposed in his papers on relational database theory. Here is one way to code this operation in SQL.

Do we look only for an exact match, or can a document have more keywords? Fortunately, the operation of picking the documents that contain all the search words is known as Relational Division. It was one of the original operators that Ted Codd proposed in his papers on relational database theory. Here is one way to code this operation in SQL. word) >= (SELECT COUNT(word) FROM SearchList); What this does is map the search list to the document's key word list and if the search list is the same size as the mapping, you have a match.

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