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will always return this row. On the other hand, FETCH RELATIVE 10 points to the Orlando row, which is the tenth row in the cursor s query results. However, if RELATIVE were used in a FETCH statement other than the first one, FETCH RELATIVE 10 would probably be pointing to a different row. As you can see, the six fetch orientation options provide a great deal of flexibility in moving through a cursor s query results. Keep in mind, however, that most of these options can be used in read-only cursors only, such as the CD_2 cursor we ve been looking at. The only option that can be used for updatable cursors is NEXT, which is the default fetch orientation. Now let s take a look at a few examples of FETCH statements so you can see how they can be used to retrieve data from your cursor s query results. The first FETCH statement that we ll look at uses the NEXT fetch orientation option to retrieve a row from the CD_2 cursor:
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FETCH NEXT FROM CD_2 INTO :CD, :Category, :Price, :On_Hand;
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The statement identifies the fetch orientation and the cursor name. As you ll recall, the NEXT keyword is optional because NEXT is the default fetch orientation. The statement also includes the INTO clause, which identifies the host variables that will receive values returned by the FETCH statement. There are four host variables to match the number of values returned by the FETCH statement. The number of variables must be the same as the number of columns returned by the cursor s SELECT statement, and the variables must be listed in the same order as the columns returned. Notice that the host variables are separated by commas and their names begin with colons. According to the SQL standard, host variables must begin with a colon, although this can vary from one SQL implementation to the next. Now that you ve seen how a FETCH NEXT statement works, you can create any FETCH statement for whichever fetch orientation you want to specify. Simply replace one option with the other. For example, the following FETCH statement uses the ABSOLUTE fetch orientation:
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FETCH ABSOLUTE 5 FROM CD_2 INTO :CD, :Category, :Price, :On_Hand;
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Notice that with the ABSOLUTE option, as with the RELATIVE option, you must specify a numeric value. In this case, the cursor will retrieve the fifth row from the cursor s query results. The ABSOLUTE, FIRST, and LAST options are the only fetch orientation options that will always return the same row from the cursor s query results, assuming that the data in the underlying table has not changed. On the other hand, the NEXT, PRIOR, and RELATIVE options return rows based on the cursor s last position. As a result, you want to be certain to design your cursors and your FETCH statements with positioning in mind.
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You mention that a cursor s SELECT statement is not executed until the cursor is opened. How does this affect special values such as CURRENT_USER or CURRENT_TIME Because a cursor s SELECT statement is not executed until the cursor is opened, special values are not assigned values until the cursor is opened, not when the cursor is declared. For example, if you include the CURRENT_TIME special value in your cursor s SELECT statement and declare that cursor at the beginning of your program code, the time assigned to the CURRENT_TIME value is the time when the cursor is opened, not the time when the cursor is declared. In addition, if you close and then reopen the cursor, the CURRENT_ TIME value is that time when you again open the cursor, not when it was first opened. You state that host variables are a type of parameter that is used in embedded SQL. How do host variables differ from other types of parameters For all practical purposes, a host variable is just like any other parameter. The main distinction is that a host variable is used in embedded SQL to pass values between the host language and SQL. The only other real distinction is that a colon must be added to the name of the variable. The reason that a colon must be included when used in an embedded SQL statement is to indicate that the name is a host variable and not a column. As a result, you can use variable names that are meaningful to your application without worrying about accidentally naming a variable the same as a column name. The colon has nothing to do with the variable itself, only in distinguishing it as a variable. A colon must also be used in SQL client modules. However, values are passed to modules through parameters, rather than host variables. Module parameters are essentially the same thing as host variables; only the names are different. If you were to refer to all of them as parameters, you would not be far off.
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