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Cursors

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 efficient?

Example 22-20. Two equivalent stored programs, one using INTO and the other using a cursor

CREATE PROCEDURE 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 DECLARE, OPEN, FETCH, and CLOSE statements, and we will probably only bother to do thiswhen we know that the SQL returns only one rowif 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 22-20over 11,000 executions, the INTO-based stored program was approximately 15% faster than the stored program that used an explicit cursor.

Figure 22-10. Relative performance of INTO versus CURSOR fetch

If you know that a SQL statement will return only one row, then a SELECT ... INTO statement will be slightly faster than declaring, opening, and fetching from a cursor.


Part I: Stored Programming Fundamentals

Introduction to MySQL Stored Programs

MySQL Stored Programming Tutorial

Language Fundamentals

Blocks, Conditional Statements, and Iterative Programming

Using SQL in Stored Programming

Error Handling

Part II: Stored Program Construction

Creating and Maintaining Stored Programs

Transaction Management

MySQL Built-in Functions

Stored Functions

Triggers

Part III: Using MySQL Stored Programs in Applications

Using MySQL Stored Programs in Applications

Using MySQL Stored Programs with PHP

Using MySQL Stored Programs with Java

Using MySQL Stored Programs with Perl

Using MySQL Stored Programs with Python

Using MySQL Stored Programs with .NET

Part IV: Optimizing Stored Programs

Stored Program Security

Tuning Stored Programs and Their SQL

Basic SQL Tuning

Advanced SQL Tuning

Optimizing Stored Program Code

Best Practices in MySQL Stored Program Development

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MySQL Stored Procedure Programming
MySQL Stored Procedure Programming
ISBN: 0596100892
EAN: 2147483647
Year: 2004
Pages: 208
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