SELECT 
  a.weight_modifier as modifier, 
  a.weight_modifier_type as modifier_type, 
  a.variant_id 
FROM 
  cscart_product_option_variants a 
WHERE 
  1 
  AND a.variant_id IN (1402)

Query time 0.00120

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "1.00"
    },
    "table": {
      "table_name": "a",
      "access_type": "const",
      "possible_keys": [
        "PRIMARY"
      ],
      "key": "PRIMARY",
      "used_key_parts": [
        "variant_id"
      ],
      "key_length": "3",
      "ref": [
        "const"
      ],
      "rows_examined_per_scan": 1,
      "rows_produced_per_join": 1,
      "filtered": "100.00",
      "cost_info": {
        "read_cost": "0.00",
        "eval_cost": "0.20",
        "prefix_cost": "0.00",
        "data_read_per_join": "48"
      },
      "used_columns": [
        "variant_id",
        "weight_modifier",
        "weight_modifier_type"
      ]
    }
  }
}