SELECT 
  cscart_multi_decproducts_categories.product_id, 
  GROUP_CONCAT(
    IF(
      cscart_multi_decproducts_categories.link_type = "M", 
      CONCAT(
        cscart_multi_decproducts_categories.category_id, 
        "M"
      ), 
      cscart_multi_decproducts_categories.category_id
    )
  ) AS category_ids, 
  product_position_source.position AS position 
FROM 
  cscart_multi_decproducts_categories 
  INNER JOIN cscart_multi_deccategories ON cscart_multi_deccategories.category_id = cscart_multi_decproducts_categories.category_id 
  AND cscart_multi_deccategories.storefront_id IN (0, 1) 
  AND (
    cscart_multi_deccategories.usergroup_ids = '' 
    OR FIND_IN_SET(
      0, cscart_multi_deccategories.usergroup_ids
    ) 
    OR FIND_IN_SET(
      1, cscart_multi_deccategories.usergroup_ids
    )
  ) 
  AND cscart_multi_deccategories.status IN ('A', 'H') 
  LEFT JOIN cscart_multi_decproducts_categories AS product_position_source ON cscart_multi_decproducts_categories.product_id = product_position_source.product_id 
  AND product_position_source.category_id = 245 
WHERE 
  cscart_multi_decproducts_categories.product_id IN (
    94, 96, 136, 90, 95, 89, 82, 84, 85, 88, 
    47, 138, 93, 87, 139, 83, 137, 248
  ) 
GROUP BY 
  cscart_multi_decproducts_categories.product_id

Query time 0.00105

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "31.84"
    },
    "grouping_operation": {
      "using_temporary_table": true,
      "using_filesort": true,
      "cost_info": {
        "sort_cost": "0.55"
      },
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_multi_deccategories",
            "access_type": "ALL",
            "possible_keys": [
              "PRIMARY",
              "c_status",
              "p_category_id"
            ],
            "rows_examined_per_scan": 84,
            "rows_produced_per_join": 3,
            "filtered": "4.00",
            "cost_info": {
              "read_cost": "19.61",
              "eval_cost": "0.67",
              "prefix_cost": "20.28",
              "data_read_per_join": "8K"
            },
            "used_columns": [
              "category_id",
              "storefront_id",
              "usergroup_ids",
              "status"
            ],
            "attached_condition": "((`vishalecarter_multi_dec`.`cscart_multi_deccategories`.`storefront_id` in (0,1)) and ((`vishalecarter_multi_dec`.`cscart_multi_deccategories`.`usergroup_ids` = '') or find_in_set(0,`vishalecarter_multi_dec`.`cscart_multi_deccategories`.`usergroup_ids`) or find_in_set(1,`vishalecarter_multi_dec`.`cscart_multi_deccategories`.`usergroup_ids`)) and (`vishalecarter_multi_dec`.`cscart_multi_deccategories`.`status` in ('A','H')))"
          }
        },
        {
          "table": {
            "table_name": "cscart_multi_decproducts_categories",
            "access_type": "ref",
            "possible_keys": [
              "PRIMARY",
              "pt"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "category_id"
            ],
            "key_length": "3",
            "ref": [
              "vishalecarter_multi_dec.cscart_multi_deccategories.category_id"
            ],
            "rows_examined_per_scan": 2,
            "rows_produced_per_join": 0,
            "filtered": "8.21",
            "index_condition": "(`vishalecarter_multi_dec`.`cscart_multi_decproducts_categories`.`product_id` in (94,96,136,90,95,89,82,84,85,88,47,138,93,87,139,83,137,248))",
            "cost_info": {
              "read_cost": "9.00",
              "eval_cost": "0.11",
              "prefix_cost": "30.63",
              "data_read_per_join": "8"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "link_type"
            ]
          }
        },
        {
          "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",
              "vishalecarter_multi_dec.cscart_multi_decproducts_categories.product_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 0,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "0.55",
              "eval_cost": "0.11",
              "prefix_cost": "31.29",
              "data_read_per_join": "8"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "position"
            ]
          }
        }
      ]
    }
  }
}