SELECT 
  * 
FROM 
  cscart_product_feature_variants 
WHERE 
  variant_id IN (
    1, 125, 211, 318, 121, 127, 149, 120, 152, 
    146, 59, 58, 147, 35, 36, 165, 320
  )

Query time 0.00032

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "11.91"
    },
    "table": {
      "table_name": "cscart_product_feature_variants",
      "access_type": "range",
      "possible_keys": [
        "PRIMARY"
      ],
      "key": "PRIMARY",
      "used_key_parts": [
        "variant_id"
      ],
      "key_length": "3",
      "rows_examined_per_scan": 17,
      "rows_produced_per_join": 17,
      "filtered": "100.00",
      "index_condition": "(`test_uchur_k`.`cscart_product_feature_variants`.`variant_id` in (1,125,211,318,121,127,149,120,152,146,59,58,147,35,36,165,320))",
      "cost_info": {
        "read_cost": "10.21",
        "eval_cost": "1.70",
        "prefix_cost": "11.91",
        "data_read_per_join": "26K"
      },
      "used_columns": [
        "variant_id",
        "feature_id",
        "url",
        "color",
        "position",
        "abt__ut2_color_style",
        "abt__ut2_multicolor"
      ]
    }
  }
}