SELECT 
  products_categories.product_id, 
  GROUP_CONCAT(
    IF(
      products_categories.link_type = "M", 
      CONCAT(
        products_categories.category_id, 
        "M"
      ), 
      products_categories.category_id
    )
  ) AS category_ids, 
  product_position_source.position AS position 
FROM 
  products_categories 
  INNER JOIN categories ON categories.category_id = products_categories.category_id 
  AND categories.storefront_id IN (0, 1) 
  AND (
    categories.usergroup_ids = '' 
    OR FIND_IN_SET(0, categories.usergroup_ids) 
    OR FIND_IN_SET(1, categories.usergroup_ids)
  ) 
  AND categories.status IN ('A', 'H') 
  LEFT JOIN products_categories AS product_position_source ON products_categories.product_id = product_position_source.product_id 
  AND product_position_source.category_id = 20331 
WHERE 
  products_categories.product_id IN (
    276551, 279095, 276805, 276567, 276811, 
    276574, 276560, 276580, 276566, 279097, 
    276812, 276815, 276803, 276804, 279104, 
    276577, 279099, 276569, 279103, 276802, 
    276556, 276807
  ) 
GROUP BY 
  products_categories.product_id

Query time 0.00255

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "59.73"
    },
    "grouping_operation": {
      "using_filesort": false,
      "nested_loop": [
        {
          "table": {
            "table_name": "products_categories",
            "access_type": "range",
            "possible_keys": [
              "PRIMARY",
              "link_type",
              "pt"
            ],
            "key": "pt",
            "used_key_parts": [
              "product_id"
            ],
            "key_length": "3",
            "rows_examined_per_scan": 66,
            "rows_produced_per_join": 66,
            "filtered": "100.00",
            "using_index": true,
            "cost_info": {
              "read_cost": "6.93",
              "eval_cost": "6.60",
              "prefix_cost": "13.53",
              "data_read_per_join": "1K"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "link_type"
            ],
            "attached_condition": "(`goimagine`.`products_categories`.`product_id` in (276551,279095,276805,276567,276811,276574,276560,276580,276566,279097,276812,276815,276803,276804,279104,276577,279099,276569,279103,276802,276556,276807))"
          }
        },
        {
          "table": {
            "table_name": "product_position_source",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY",
              "pt"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "category_id",
              "product_id"
            ],
            "key_length": "6",
            "ref": [
              "const",
              "goimagine.products_categories.product_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 66,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "16.50",
              "eval_cost": "6.60",
              "prefix_cost": "36.63",
              "data_read_per_join": "1K"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "position"
            ]
          }
        },
        {
          "table": {
            "table_name": "categories",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY",
              "c_status",
              "p_category_id"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "category_id"
            ],
            "key_length": "3",
            "ref": [
              "goimagine.products_categories.category_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 3,
            "filtered": "5.00",
            "cost_info": {
              "read_cost": "16.50",
              "eval_cost": "0.33",
              "prefix_cost": "59.73",
              "data_read_per_join": "8K"
            },
            "used_columns": [
              "category_id",
              "usergroup_ids",
              "status",
              "storefront_id"
            ],
            "attached_condition": "((`goimagine`.`categories`.`storefront_id` in (0,1)) and ((`goimagine`.`categories`.`usergroup_ids` = '') or (0 <> find_in_set(0,`goimagine`.`categories`.`usergroup_ids`)) or (0 <> find_in_set(1,`goimagine`.`categories`.`usergroup_ids`))) and (`goimagine`.`categories`.`status` in ('A','H')))"
          }
        }
      ]
    }
  }
}