SELECT 
  category_id, 
  yml2_market_category 
FROM 
  cscart_categories 
WHERE 
  category_id IN ('487', '750') 
  AND yml2_market_category != ''

Query time 0.00037

JSON explain

{
  "query_block": {
    "select_id": 1,
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_categories",
          "access_type": "range",
          "possible_keys": ["PRIMARY", "p_category_id"],
          "key": "PRIMARY",
          "key_length": "3",
          "used_key_parts": ["category_id"],
          "rows": 2,
          "filtered": 100,
          "index_condition": "cscart_categories.category_id in ('487','750')",
          "attached_condition": "cscart_categories.yml2_market_category <> ''"
        }
      }
    ]
  }
}