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POMysql query dont't uses index when there are variables in WHERE
 

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  1. POMysql query dont't uses index when there are variables in WHERE
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    <p>I have this table:</p> <pre><code>CREATE TABLE `ClientesHora_copy` ( `dia` varchar(6) default NULL, `hora` varchar(2) default NULL, `sit` varchar(17) default NULL, `nodo` varchar(6) default NULL, `clientes` decimal(41,0) default NULL, `segundos` double default NULL, `llamadas` decimal(41,0) default NULL, `fecha` datetime default NULL, KEY `nodo_fecha` (`nodo`,`fecha`), KEY `nodo` (`nodo`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 </code></pre> <p>and this query:</p> <pre><code>SET @sitio= 'ABA000'; SET @horaini='2013-02-12 15:18:00'; SET @horafin='2013-02-12 20:36:00'; EXPLAIN SELECT nodo,sit,clientes,segundos,llamadas,fecha,hora,@horaini AS horaini,@horafin AS horafin FROM `ClientesHora_copy` WHERE nodo =@sitio AND fecha BETWEEN DATE_SUB(DATE_FORMAT(@horaini, "%Y-%m-%d %H:00:00"), INTERVAL 7 DAY) AND DATE_SUB(DATE_FORMAT(@horafin, "%Y-%m-%d %H:00:00"), INTERVAL 7 DAY) </code></pre> <p>I have this in explain</p> <pre><code>id select_type table type possible_keys key key_len ref rows Extra ------ ----------- ----------------- ------ ------------- ------ ------- ------ ------- ------------- 1 SIMPLE ClientesHora_copy ALL (NULL) (NULL) (NULL) (NULL) 2716460 Using where </code></pre> <p>But if I dont use the @sitio variable (but use the @horaini, @horafin variables):</p> <pre><code>EXPLAIN SELECT nodo,sit,clientes,segundos,llamadas,fecha,hora,@horaini AS horaini,@horafin AS horafin FROM `ClientesHora_copy` WHERE nodo ='ABA000' AND fecha BETWEEN DATE_SUB(DATE_FORMAT(@horaini, "%Y-%m-%d %H:00:00"), INTERVAL 7 DAY) AND DATE_SUB(DATE_FORMAT(@horafin, "%Y-%m-%d %H:00:00"), INTERVAL 7 DAY) </code></pre> <p>I get this:</p> <pre><code>id select_type table type possible_keys key key_len ref rows Extra ------ ----------- ----------------- ------ --------------- ---------- ------- ------ ------ ------------- 1 SIMPLE ClientesHora_copy range nodo_fecha,nodo nodo_fecha 18 (NULL) 1 Using where </code></pre> <p>Any idea of why Mysql doesnt use the index with the @sitio variable but it does with @fechaini and @fechafin?</p> <p>Thanks!</p>
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    1. This table or related slice is empty.
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    1. USAlejandro
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      1. VTUpMod
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    1. COThe problem isn't the lack of a "constant" value (as the selected answer indicates. It's fairly easy to demonstrate the MySQL will use an index "const" ref with a user variable. The problem is the character set; the user variable is likely a different characterset than the column. We can use the `CONVERT()` function can be used to convert between different character sets.
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      1. USspencer7593
 

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