SELECT 
  variant_id 
FROM 
  cscart_product_variation_disabled_variants 
WHERE 
  group_id = 3059

Query time 0.00121

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "41.93"
    },
    "table": {
      "table_name": "cscart_product_variation_disabled_variants",
      "access_type": "ALL",
      "rows_examined_per_scan": 409,
      "rows_produced_per_join": 40,
      "filtered": "10.00",
      "cost_info": {
        "read_cost": "37.84",
        "eval_cost": "4.09",
        "prefix_cost": "41.93",
        "data_read_per_join": "30K"
      },
      "used_columns": [
        "group_id",
        "variant_id"
      ],
      "attached_condition": "(`chocoramo`.`cscart_product_variation_disabled_variants`.`group_id` = 3059)"
    }
  }
}