SELECT 
  cscart_products_categories.product_id, 
  GROUP_CONCAT(
    IF(
      cscart_products_categories.link_type = "M", 
      CONCAT(
        cscart_products_categories.category_id, 
        "M"
      ), 
      cscart_products_categories.category_id
    )
  ) AS category_ids, 
  product_position_source.position AS position 
FROM 
  cscart_products_categories 
  INNER JOIN cscart_categories ON cscart_categories.category_id = cscart_products_categories.category_id 
  AND cscart_categories.storefront_id IN (0, 1) 
  AND (
    cscart_categories.usergroup_ids = '' 
    OR FIND_IN_SET(
      0, cscart_categories.usergroup_ids
    ) 
    OR FIND_IN_SET(
      1, cscart_categories.usergroup_ids
    )
  ) 
  AND cscart_categories.status IN ('A', 'H') 
  LEFT JOIN cscart_products_categories AS product_position_source ON cscart_products_categories.product_id = product_position_source.product_id 
  AND product_position_source.category_id = 266 
WHERE 
  cscart_products_categories.product_id IN (
    381712, 339825, 430703, 430845, 431042, 
    431200, 430885, 381711, 430865, 430976, 
    431316, 430887, 430904, 430936, 430992, 
    431238, 431251, 431393, 339855, 430661, 
    430753, 430756, 430836, 431003, 431046, 
    431061, 430801, 430810, 430866, 430939, 
    431011, 431029, 431072, 431171, 431193, 
    431333, 430932, 430788, 430809, 430999, 
    431052, 431192, 431205, 430905, 430910, 
    430927, 430749, 430862, 431062, 431463, 
    339726, 430634, 430794, 430870, 431039, 
    431091, 431314, 431024, 431315, 431327, 
    430677, 430704, 430714, 430853, 430888, 
    430923, 431098, 431242, 430687, 431028, 
    430641, 430675, 430707, 430713, 430851, 
    430895, 431112, 431326, 431339, 430694, 
    430708, 430738, 430782, 430811, 430827, 
    430861, 430874, 430937, 431077, 431308, 
    431365, 339838, 431245, 339841, 430855, 
    431054, 430800, 430852, 430863, 431129
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00204

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "281.15"
    },
    "grouping_operation": {
      "using_filesort": false,
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_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": 100,
            "rows_produced_per_join": 100,
            "filtered": "100.00",
            "using_index": true,
            "cost_info": {
              "read_cost": "21.15",
              "eval_cost": "20.00",
              "prefix_cost": "41.15",
              "data_read_per_join": "1K"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "link_type"
            ],
            "attached_condition": "(`webmarco`.`cscart_products_categories`.`product_id` in (381712,339825,430703,430845,431042,431200,430885,381711,430865,430976,431316,430887,430904,430936,430992,431238,431251,431393,339855,430661,430753,430756,430836,431003,431046,431061,430801,430810,430866,430939,431011,431029,431072,431171,431193,431333,430932,430788,430809,430999,431052,431192,431205,430905,430910,430927,430749,430862,431062,431463,339726,430634,430794,430870,431039,431091,431314,431024,431315,431327,430677,430704,430714,430853,430888,430923,431098,431242,430687,431028,430641,430675,430707,430713,430851,430895,431112,431326,431339,430694,430708,430738,430782,430811,430827,430861,430874,430937,431077,431308,431365,339838,431245,339841,430855,431054,430800,430852,430863,431129))"
          }
        },
        {
          "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",
              "webmarco.cscart_products_categories.product_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 100,
            "filtered": "100.00",
            "cost_info": {
              "read_cost": "100.00",
              "eval_cost": "20.00",
              "prefix_cost": "161.15",
              "data_read_per_join": "1K"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "position"
            ]
          }
        },
        {
          "table": {
            "table_name": "cscart_categories",
            "access_type": "eq_ref",
            "possible_keys": [
              "PRIMARY",
              "c_status",
              "p_category_id"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "category_id"
            ],
            "key_length": "3",
            "ref": [
              "webmarco.cscart_products_categories.category_id"
            ],
            "rows_examined_per_scan": 1,
            "rows_produced_per_join": 5,
            "filtered": "5.00",
            "cost_info": {
              "read_cost": "100.00",
              "eval_cost": "1.00",
              "prefix_cost": "281.15",
              "data_read_per_join": "29K"
            },
            "used_columns": [
              "category_id",
              "usergroup_ids",
              "status",
              "storefront_id"
            ],
            "attached_condition": "((`webmarco`.`cscart_categories`.`storefront_id` in (0,1)) and ((`webmarco`.`cscart_categories`.`usergroup_ids` = '') or find_in_set(0,`webmarco`.`cscart_categories`.`usergroup_ids`) or find_in_set(1,`webmarco`.`cscart_categories`.`usergroup_ids`)) and (`webmarco`.`cscart_categories`.`status` in ('A','H')))"
          }
        }
      ]
    }
  }
}