When you need to retrieve only a single row from a
SELECT statement, using the
INTO clause is far easier than
declaring, opening, fetching from, and closing a cursor. But does the
INTO clause generate some
additional work for MySQL or could the
INTO clause be more efficient than a cursor?
In other words, which of the two stored programs shown in Example 22-20 is more
using_into( p_customer_id INT,OUT p_customer_name VARCHAR(30)) READS SQL DATA BEGIN SELECT customer_name INTO p_customer_name FROM customers WHERE customer_id=p_customer_id; END; CREATE PROCEDURE
using_cursor(p_customer_id INT,OUT p_customer_name VARCHAR(30)) READS SQL DATA BEGIN DECLARE cust_csr CURSOR FOR SELECT customer_name FROM customers WHERE customer_id=p_customer_id; OPEN cust_csr; FETCH cust_csr INTO p_customer_name; CLOSE cust_csr; END;
Certainly, it is simpler to code an
INTO statement than to code
CLOSE statements, and we will probably only
bother to do this—when we know that the SQL returns only one row—if
there is a specific performance advantage. As it turns out, there is
actually a slight performance penalty for using an explicit cursor.
Figure 22-10 shows the
relative performance of each of the stored programs in Example 22-20—over 11,000
INTO-based stored program was approximately 15% faster than the stored program that used an explicit ...