SELECT 
  cscart_product_feature_variant_descriptions.variant, 
  cscart_product_feature_variants.variant_id, 
  cscart_product_feature_variants.feature_id, 
  cscart_product_features_values.variant_id as selected, 
  cscart_product_features.feature_type 
FROM 
  cscart_product_feature_variants 
  LEFT JOIN cscart_product_feature_variant_descriptions ON cscart_product_feature_variant_descriptions.variant_id = cscart_product_feature_variants.variant_id 
  AND cscart_product_feature_variant_descriptions.lang_code = 'en' 
  INNER JOIN cscart_product_features_values ON cscart_product_features_values.variant_id = cscart_product_feature_variants.variant_id 
  AND cscart_product_features_values.lang_code = 'en' 
  AND cscart_product_features_values.product_id = 250 
  AND cscart_product_features_values.feature_id = cscart_product_feature_variants.feature_id 
  LEFT JOIN cscart_product_features ON cscart_product_features.feature_id = cscart_product_feature_variants.feature_id 
WHERE 
  1 
  AND cscart_product_feature_variants.feature_id IN (
    23, 21, 26, 25, 27, 29, 35, 32, 31, 42, 45, 
    44, 43
  ) 
GROUP BY 
  cscart_product_feature_variants.variant_id 
ORDER BY 
  cscart_product_feature_variants.position, 
  cscart_product_feature_variant_descriptions.variant

Query time 0.00500

JSON explain

{
  "query_block": {
    "select_id": 1,
    "filesort": {
      "sort_key": "cscart_product_feature_variants.position, cscart_product_feature_variant_descriptions.variant",
      "temporary_table": {
        "nested_loop": [
          {
            "table": {
              "table_name": "cscart_product_features_values",
              "access_type": "ref",
              "possible_keys": [
                "PRIMARY",
                "fl",
                "variant_id",
                "lang_code",
                "product_id",
                "fpl",
                "idx_product_feature_variant_id"
              ],
              "key": "idx_product_feature_variant_id",
              "key_length": "3",
              "used_key_parts": ["product_id"],
              "ref": ["const"],
              "rows": 54,
              "filtered": 46.73684311,
              "attached_condition": "cscart_product_features_values.product_id <=> 250 and cscart_product_features_values.lang_code = 'en'",
              "using_index": true
            }
          },
          {
            "table": {
              "table_name": "cscart_product_feature_variants",
              "access_type": "eq_ref",
              "possible_keys": ["PRIMARY", "feature_id"],
              "key": "PRIMARY",
              "key_length": "3",
              "used_key_parts": ["variant_id"],
              "ref": ["cscart.cscart_product_features_values.variant_id"],
              "rowid_filter": {
                "range": {
                  "key": "feature_id",
                  "used_key_parts": ["feature_id"]
                },
                "rows": 35,
                "selectivity_pct": 22.15189873
              },
              "rows": 1,
              "filtered": 100,
              "attached_condition": "cscart_product_feature_variants.feature_id = cscart_product_features_values.feature_id and cscart_product_feature_variants.feature_id in (23,21,26,25,27,29,35,32,31,42,45,44,43)"
            }
          },
          {
            "table": {
              "table_name": "cscart_product_features",
              "access_type": "eq_ref",
              "possible_keys": ["PRIMARY"],
              "key": "PRIMARY",
              "key_length": "3",
              "used_key_parts": ["feature_id"],
              "ref": ["cscart.cscart_product_features_values.feature_id"],
              "rows": 1,
              "filtered": 100
            }
          },
          {
            "table": {
              "table_name": "cscart_product_feature_variant_descriptions",
              "access_type": "eq_ref",
              "possible_keys": ["PRIMARY"],
              "key": "PRIMARY",
              "key_length": "9",
              "used_key_parts": ["variant_id", "lang_code"],
              "ref": ["cscart.cscart_product_features_values.variant_id", "const"],
              "rows": 1,
              "filtered": 100,
              "attached_condition": "trigcond(cscart_product_feature_variant_descriptions.lang_code = 'en')"
            }
          }
        ]
      }
    }
  }
}