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List the offices where there is a salesperson whose quota represents more than 55 percent of the office s target.
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SELECT CITY FROM OFFICES WHERE EXISTS (SELECT FROM WHERE AND CITY -------Denver Atlanta
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* SALESREPS REP_OFFICE = OFFICE QUOTA > (.55 * TARGET))
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Note that in each of these examples, the subquery includes an outer reference to a column of the table in the main query. In practice, the subquery in an EXISTS test will always contain an outer reference that links the subquery to the row currently being tested by the main query.
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Quantified Tests (ANY and ALL) *
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The subquery version of the IN test checks whether a data value is equal to some value in a column of subquery results. SQL provides two quantified tests, ANY and ALL, that extend this notion to other comparison operators, such as greater than (>) and less than (<). Both of these tests compare a data value to the column of data values produced by a subquery, as shown in Figure 9-6.
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Figure 9-6.
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Subqueries and Query Expressions
The ANY Test *
The ANY test is used in conjunction with one of the six SQL comparison operators (=, <>, <, <=, >, >=) to compare a single test value to a column of data values produced by a subquery. To perform the test, SQL uses the specified comparison operator to compare the test value to each data value in the column, one at a time. If any of the individual comparisons yield a TRUE result, the ANY test returns a TRUE result. Here is an example of a request that can be handled with the ANY test: List the salespeople who have taken an order that represents more than 10 percent of their quota.
RETRIEVING DATA SELECT NAME FROM SALESREPS WHERE (.1 * QUOTA) < ANY (SELECT AMOUNT FROM ORDERS WHERE REP = EMPL_NUM) NAME -------------Sam Clark Larry Fitch Nancy Angelli
Conceptually, the main query tests each row of the SALESREPS table, one by one. The subquery finds all of the orders taken by the current salesperson and returns a column containing the order amounts for those orders. The WHERE clause of the main query then computes 10 percent of the current salesperson s quota and uses it as a test value, comparing it to every order amount produced by the subquery. If any order amount exceeds the calculated test value, the ANY test returns TRUE, and the salesperson is included in the query results. If not, the salesperson is not included in the query results. The keyword SOME is an alternative for ANY specified by the ANSI/ISO SQL standard. Either keyword can generally be used, but some DBMS brands do not support SOME. The ANY test can sometimes be difficult to understand because it involves an entire set of comparisons, not just one. It helps if you read the test in a slightly different way than it appears in the statement. If this ANY test appears:
WHERE X < ANY (SELECT Y )
instead of reading the test like this:
"where X is less than any select Y "
SQL: The Complete Reference
try reading it like this:
"where, for some Y, X is less than Y"
When you use this trick, the preceding query becomes: Select the salespeople where, for some order taken by the salesperson, 10 percent of the salesperson s quota is less than the order amount. If the subquery in an ANY test produces no rows of query results, or if the query results include NULL values, the operation of the ANY test may vary from one DBMS to another. The ANSI/ISO SQL standard specifies these detailed rules describing the results of the ANY test when the test value is compared to the column of subquery results: I If the subquery produces an empty column of query results, the ANY test returns FALSE there is no value produced by the subquery for which the comparison test holds. I If the comparison test is TRUE for at least one of the data values in the column, then the ANY search condition returns TRUE there is indeed some value produced by the subquery for which the comparison test holds. I If the comparison test is FALSE for every data value in the column, then the ANY search condition returns FALSE. In this case, you can conclusively state that there is no value produced by the subquery for which the comparison test holds. I If the comparison test is not TRUE for any data value in the column, but it is NULL (unknown) for one or more of the data values, then the ANY search condition returns NULL. In this situation, you cannot conclusively state whether there is a value produced by the subquery for which the comparison test holds; there may or may not be, depending on the actual (but currently unknown) values for the NULL data. The ANY comparison operator can be very tricky to use in practice, especially in conjunction with the inequality (<>) comparison operator. Here is an example that shows the problem: List the names and ages of all the people in the sales force who do not manage an office. It s tempting to express this query as shown in this example:
SELECT NAME, AGE FROM SALESREPS WHERE EMPL_NUM <> ANY (SELECT MGR FROM OFFICES)
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