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SELECT 
  * 
FROM 
  cscart_logos 
WHERE 
  IF(
    layout_id = 0, 
    1, 
    IF(layout_id = 1, 1, 0)
  ) 
  AND IF(
    style_id = '', 
    1, 
    IF(style_id = 'RusCaviar', 1, 0)
  ) 
  AND company_id = 1

Query time 0.00034

Explain
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	cscart_logos	ALL					13	Using where

Result

logo_id	layout_id	style_id	company_id	type
7	0		1	gift_cert
8	1	RusCaviar	1	theme
9	1	RusCaviar	1	mail
10	1	RusCaviar	1	favicon