Select com pivot lento...

[Dennys Fredericci]

Oi Pessoal!

Estou tendo problemas de performance com o select abaixo:

Ele retorna aproximadamente 740938 linhas. Eu acredito que o problema esteja no subselect.

Como posso melhorar este select?

Obrigado!


SELECT timesec,

(SELECT a.value FROM historicotags a WHERE a.idtag = 663 AND a.timesec <=
h.timesec ORDER BY a.timesec desc LIMIT 1) as '663' ,

(SELECT a.value FROM historicotags a WHERE a.idtag = 724 AND a.timesec <=
h.timesec ORDER BY a.timesec desc LIMIT 1) as '724' ,

(SELECT a.value FROM historicotags a WHERE a.idtag = 685 AND a.timesec <=
h.timesec ORDER BY a.timesec desc LIMIT 1) as '685' ,

(SELECT a.value FROM historicotags a WHERE a.idtag = 684 AND a.timesec <=
h.timesec ORDER BY a.timesec desc LIMIT 1) as '684' ,

(SELECT a.value FROM historicotags a WHERE a.idtag = 664 AND a.timesec <=
h.timesec ORDER BY a.timesec desc LIMIT 1) as '664' ,

(SELECT a.value FROM historicotags a WHERE a.idtag = 922 AND a.timesec <=
h.timesec ORDER BY a.timesec desc LIMIT 1) as '922' ,

(SELECT a.value FROM historicotags a WHERE a.idtag = 923 AND a.timesec <=
h.timesec ORDER BY a.timesec desc LIMIT 1) as '923' ,

(SELECT a.value FROM historicotags a WHERE a.idtag = 924 AND a.timesec <=
h.timesec ORDER BY a.timesec desc LIMIT 1) as '924'

FROM historicoTags h WHERE timesec between 1295488800 AND 1295551799 GROUP
BY timesec;