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Of course, it would be unusual to call this procedure with a literal customer number, but it s perfectly legal since that is an input parameter. The remaining three parameters have acceptable data assignment targets (in this case, they are PL/SQL variables) passed to them so that they can receive the returned values. Here is an illegal call to the same procedure:
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/* Get the customer info for customer 2111 */ execute get_cust_info(2111, XYZ Co , the_rep, the_city)
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because the second parameter is an output parameter and cannot receive a literal value. In addition to input and output parameters, Oracle allows you to specify procedure parameters that are both input and output (INOUT) parameters. They must obey the same previously cited restrictions for output parameters, but in addition, their values are used as input by the procedure. Figure 20-10 shows a version of the GET_CUST_INFO procedure defined in the Transact-SQL dialect. The way in which the output parameters are identified in the procedure header differs slightly from the Oracle version, and the single-row SELECT statement has a different form. Otherwise, the structure of the procedure and its operation are identical to the Oracle example.
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/* Get customer name, sales rep and office */ create procedure get_cust_info(c_num in integer, c_name out varchar(20), r_name out varchar(15), c_offc out varchar(15)) as begin /* Simple single-row query to get info */ select company, name, city into c_name, r_name, c_offc from customers, salesreps, offices where cust_num = c_num and empl_num = cust_rep and office = rep_office; end;
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Transact-SQL stored procedure with output parameters
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When this procedure is called from another Transact-SQL procedure, the fact that the second, third, and fourth parameters are output parameters must be indicated in the call to the procedure, as well as in its definition. Here is the Transact-SQL syntax for calling the procedure in Figure 20-10:
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/* Get the customer info for customer 2111 */ declare the_name varchar(20); declare the_rep varchar(15); declare the_city varchar(15); exec get_cust_info @c_num = 2111, @c_name = the_name output, @r_name = the_rep output, @c_offc = the_city output
Figure 20-11 shows the Informix SPL version of the same stored procedure example. Informix takes a different approach to handling multiple return values. Instead of output parameters, Informix extends the definition of a stored function to allow multiple return values. Thus, the GET_CUST_INFO procedure becomes a function for the Informix dialect. The multiple return values are specified in the RETURNING clause of the procedure header, and they are actually returned by the RETURN statement.
/* Get customer name, sales rep and office */ create function get_cust_info(c_num integer) returning varchar(20), varchar(15), varchar(15) define c_name varchar(20); define r_name varchar(15); define c_offc varchar(15); /* Simple single-row query to get info */ select company, name, city into cname, r_name, c_offc from customers, salesreps, offices where cust_num = c_num and empl_num = cust_rep and office = rep_office; /* Return the three values */ return cname, r_name, c_offc; end procedure;
Figure 20-11.
Informix stored function with multiple return values
20:
Database Processing and Stored Procedures
The Informix CALL statement that invokes the stored function uses a special RETURNING clause to receive the returned values:
/* Get the customer info for customer 2111 */ define the_name varchar(20); define the_rep varchar(15); define the_city varchar(15); call get_cust_info (2111) returning the_name, the_rep, the_city;
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As in the Transact-SQL dialect, Informix also allows a version of the CALL statement that passes the parameters by name:
call get_cust_info (c_num = 2111) returning the_name, the_rep, the_city;
Conditional Execution
One of the most basic features of stored procedures is an IF THEN ELSE construct for decision making within the procedure. Look back at the original ADD_CUST procedure defined in Figure 20-1 for adding a new customer. Suppose that the rules for adding new customers are modified so that there is a cap on the amount by which a salesperson s quota should be increased for a new customer. If the customer s anticipated first-year orders are $20,000 or less, that amount should be added to the quota, but if they are more than $20,000, the quota should be increased by only $20,000. Figure 20-12 shows a modified procedure that implements this new policy. The IF THEN ELSE logic operates exactly as it does in any conventional programming language. All of the stored procedure dialects allow nested IF statements for more complex decision making. Several provide extended conditional logic to streamline multiway branching. For example, suppose you wanted to do three different things within the ADD_CUST stored procedure, depending on whether the customer s anticipated firstyear orders are under $20,000, between $20,000 and $50,000, or over $50,000. In Oracle s PL/SQL, you could express the three-way decision this way:
/* Process sales target by range */ if tgt_sls < 20000.00 then /* Handle low-target customers here */ . . . elsif tgt_sls < 50000.00 then /* Handle mid-target customers here */ . . . else /* Handle high-target customers here */ . . . end if;
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