MySQL的不使用功能指標

Question

我有簡單的功能由一個SQL查詢

CREATE FUNCTION `GetProductIDFunc`(in_title char (14)) 
     RETURNS bigint(20) 
BEGIN 
    declare out_id bigint;  

    select id into out_id from products where title = in_title limit 1;  
    RETURN out_id; 
END 

該函數的執行時間需要5秒

的

select Benchmark(500 ,GetProductIdFunc('sample_product')); 

平原查詢的執行時間花費0.001秒

select Benchmark(500,(select id from products where title = 'sample_product' limit 1)); 

「標題」字段被索引。爲什麼功能執行需要很多時間，我如何優化它？

編輯： 執行計劃

mysql> EXPLAIN EXTENDED select id from products where title = 'sample_product' limit 1; 
+----+-------------+----------+-------+---------------+------------+---------+-------+------+----------+-------------+ 
| id | select_type | table | type | possible_keys | key  | key_len | ref | rows | filtered | Extra  | 
+----+-------------+----------+-------+---------------+------------+---------+-------+------+----------+-------------+ 
| 1 | SIMPLE  | products | const | Index_title | Index_title | 14  | const | 1 | 100.00 | Using index | 
+----+-------------+----------+-------+---------------+------------+---------+-------+------+----------+-------------+ 
1 row in set, 1 warning (0.00 sec) 

mysql> EXPLAIN select GetProductIdFunc('sample_product'); 
+----+-------------+-------+------+---------------+------+---------+------+------+----------------+ 
| id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra   | 
+----+-------------+-------+------+---------------+------+---------+------+------+----------------+ 
| 1 | SIMPLE  | NULL | NULL | NULL   | NULL | NULL | NULL | NULL | No tables used | 
+----+-------------+-------+------+---------------+------+---------+------+------+----------------+ 
1 row in set (0.00 sec) 

Answer 1

這可能是一個字符集問題。如果該函數使用與表列不同的字符集，則儘管存在索引，但仍會導致性能非常低下。

運行show create table products\G來確定列的字符集。

運行show variables like 'character_set%';查看相關的默認字符集是爲您的數據庫。

Answer 2

試試這個：

CREATE FUNCTION `GetProductIDFunc`(in_title char (14)) 
     RETURNS bigint(20) 
BEGIN 
    declare out_id bigint;  

    set out_id = (select id from products where title = in_title limit 1);  
    RETURN out_id; 
END