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SQL: A Beginner s Guide
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How does the ORDER BY clause affect query results in embedded SQL and SQL modules You can use the ORDER BY clause only in direct invocation and when defining cursors. (I discuss cursors in 15.) You cannot use an ORDER BY clause in other situations. This is because of limitations in application languages they cannot handle an unknown number of rows in a query result. Application languages do not know what to do with this sort of uncertainty. And because the ORDER BY clause applies only to multirow query results, the clause is not applicable to environments that require rows to be returned one at a time. However, cursors offer a way for application languages to deal with that uncertainty, allowing the ORDER BY clause to be used in cursor definitions. Cursors are discussed in more detail in 15.
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As you can see, the rows are listed according to the order of the PRICE values, which are in ascending order. In addition, the ON_HAND values are listed in descending order for each price. So for the set of 14.99 PRICE values, the rows start with a value of 42 in the ON_HAND column and end with a value of 5. Then we jump to the next group of PRICE values: 15.99. Once again, the largest ON_HAND value for the 15.99 PRICE range is listed first and the last row contains the smallest ON_HAND value for the 15.99 PRICE range. Whenever you re using the ORDER BY clause, you must be aware of the order in which you list column names within that clause. In the preceding example, the PRICE column is listed first, so the rows are ordered first by the PRICE column and then by the ON_HAND column. However, you can reverse the column names, as shown in the following SELECT statement:
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SELECT * FROM COMPACT_DISC_STOCK WHERE PRICE < 16.00 ORDER BY ON_HAND, PRICE DESC;
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This time, the ON_HAND column is listed first and the PRICE column listed second, and the PRICE column is assigned the DESC keyword. As a result, the rows will be sorted by the ON_HAND column first, as shown in the following query results:
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COMPACT_DISC ------------------------------------Orlando Kojiki That Christmas Feeling Leonard Cohen The Best Of Past Light Court and Spark Carreras Domingo Pavarotti in Concert CATEGORY -----------Instrumental Instrumental Vocal Vocal Instrumental Vocal Vocal PRICE ----14.99 15.99 14.99 15.99 15.99 14.99 15.99 ON_HAND ------5 6 8 12 17 22 27
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Blues on the Bayou Fundamental Blue
Vocal Vocal Vocal
14.99 15.99 14.99
27 34 42
Notice that the ON_HAND values are in ascending order. The rows are then ordered according to the PRICE value. However, because there are only two rows that share the same ON_HAND value (27), these are the only rows that the ORDER BY column affects, with regard to the PRICE column. The ORDER BY clause is a convenient tool for organizing your query results, but remember, it doesn t affect which data is displayed. Only the other clauses can actually name, filter, and group data. The ORDER BY clause is merely an organizer for what already exists. And in fact, while it is not a very sound practice, you can include columns in the ORDER BY clause that are not in the SELECT clause, thereby sorting on columns that are not visible in the query results.
Try This 7-1
Querying the Inventory Database
For the Try This exercises in previous chapters, you created a number of persistent base tables that are capable of storing data. In this chapter, you learned how to create SELECT statements that allow you to query data in base tables. As a result, this exercise focuses on creating SELECT statements that query data in the tables that you created. However, before you can actually query those tables, data must be stored within them. While I do not cover inserting data until 8, I do provide the statements you need to insert the data in the Try_This_ 07.txt file, which you can download from our web site. The file contains a series of INSERT statements that allow you to populate the tables, along with the SELECT statements used in this exercise. You can also view these statements in Appendix C. If you look at the Try_This_07.txt file, you ll see a series of INSERT statements that are grouped together according to the tables that you created in the INVENTORY database. For example, the first set of INSERT statements are for the CD_LABELS table, as shown in the following statements:
--Insert data into the CD_LABELS table INSERT INTO CD_LABELS VALUES ( 827, 'Private Music' ); INSERT INTO CD_LABELS VALUES ( 828, 'Reprise Records' ); INSERT INTO CD_LABELS VALUES ( 829, 'Asylum Records' ); INSERT INTO CD_LABELS VALUES ( 830, 'Windham Hill Records' ); INSERT INTO CD_LABELS VALUES ( 831, 'Geffen' ); INSERT INTO CD_LABELS VALUES ( 832, 'MCA Records' ); INSERT INTO CD_LABELS VALUES ( 833, 'Decca Record Company' ); INSERT INTO CD_LABELS VALUES ( 834, 'CBS Records' ); INSERT INTO CD_LABELS VALUES ( 835, 'Capitol Records' ); INSERT INTO CD_LABELS VALUES ( 836, 'Sarabande Records' ); --End inserts for the CD_LABELS table
You will need to copy these statements into your client application and execute them. Each INSERT statement adds one row of data to the applicable table. For example, the first INSERT statement listed in the preceding code adds one row of data to the
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