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 
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') 
WHERE 
  cscart_products_categories.product_id IN (
    969, 
    970, 
    636, 
    637, 
    972, 
    973, 
    974, 
    975, 
    945, 
    946, 
    953, 
    954, 
    955, 
    956, 
    957, 
    958, 
    699, 
    700, 
    701, 
    702, 
    774, 
    775, 
    776, 
    777, 
    778, 
    779, 
    780, 
    781, 
    782, 
    783, 
    784, 
    785, 
    786, 
    787, 
    788, 
    789, 
    790, 
    791, 
    792, 
    793, 
    794, 
    795, 
    678, 
    679, 
    680, 
    564, 
    565, 
    566, 
    567, 
    568, 
    569, 
    570, 
    571, 
    572, 
    573, 
    574, 
    575, 
    576, 
    577, 
    578, 
    579, 
    580, 
    581, 
    582, 
    583, 
    584, 
    585, 
    586, 
    592, 
    593, 
    827, 
    828, 
    829, 
    830, 
    831, 
    832, 
    833, 
    834, 
    835, 
    837, 
    838, 
    839, 
    840, 
    841, 
    842, 
    843, 
    844, 
    845, 
    846, 
    847, 
    848, 
    849, 
    850, 
    851, 
    852, 
    853, 
    854, 
    855, 
    856, 
    857, 
    858, 
    859, 
    860, 
    861, 
    862, 
    863, 
    864, 
    865, 
    866, 
    867, 
    868, 
    869, 
    870, 
    871, 
    872, 
    873, 
    874, 
    875, 
    876, 
    877, 
    878, 
    811, 
    812, 
    815, 
    816, 
    817, 
    818, 
    1025, 
    1026, 
    1027
  ) 
GROUP BY 
  cscart_products_categories.product_id

Query time 0.00222

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "122.05"
    },
    "grouping_operation": {
      "using_temporary_table": true,
      "using_filesort": true,
      "cost_info": {
        "sort_cost": "17.91"
      },
      "nested_loop": [
        {
          "table": {
            "table_name": "cscart_categories",
            "access_type": "ALL",
            "possible_keys": [
              "PRIMARY",
              "c_status",
              "p_category_id"
            ],
            "rows_examined_per_scan": 125,
            "rows_produced_per_join": 5,
            "filtered": "4.00",
            "cost_info": {
              "read_cost": "29.49",
              "eval_cost": "1.00",
              "prefix_cost": "30.49",
              "data_read_per_join": "20K"
            },
            "used_columns": [
              "category_id",
              "storefront_id",
              "usergroup_ids",
              "status"
            ],
            "attached_condition": "((`cscart`.`cscart_categories`.`storefront_id` in (0,1)) and ((`cscart`.`cscart_categories`.`usergroup_ids` = '') or find_in_set(0,`cscart`.`cscart_categories`.`usergroup_ids`) or find_in_set(1,`cscart`.`cscart_categories`.`usergroup_ids`)) and (`cscart`.`cscart_categories`.`status` in ('A','H')))"
          }
        },
        {
          "table": {
            "table_name": "cscart_products_categories",
            "access_type": "ref",
            "possible_keys": [
              "PRIMARY",
              "pt"
            ],
            "key": "PRIMARY",
            "used_key_parts": [
              "category_id"
            ],
            "key_length": "3",
            "ref": [
              "cscart.cscart_categories.category_id"
            ],
            "rows_examined_per_scan": 12,
            "rows_produced_per_join": 17,
            "filtered": "29.85",
            "index_condition": "(`cscart`.`cscart_products_categories`.`product_id` in (969,970,636,637,972,973,974,975,945,946,953,954,955,956,957,958,699,700,701,702,774,775,776,777,778,779,780,781,782,783,784,785,786,787,788,789,790,791,792,793,794,795,678,679,680,564,565,566,567,568,569,570,571,572,573,574,575,576,577,578,579,580,581,582,583,584,585,586,592,593,827,828,829,830,831,832,833,834,835,837,838,839,840,841,842,843,844,845,846,847,848,849,850,851,852,853,854,855,856,857,858,859,860,861,862,863,864,865,866,867,868,869,870,871,872,873,874,875,876,877,878,811,812,815,816,817,818,1025,1026,1027))",
            "cost_info": {
              "read_cost": "61.65",
              "eval_cost": "3.58",
              "prefix_cost": "104.14",
              "data_read_per_join": "286"
            },
            "used_columns": [
              "product_id",
              "category_id",
              "link_type"
            ]
          }
        }
      ]
    }
  }
}