SELECT 
  COUNT(*) 
FROM 
  cscart_products as products 
  LEFT JOIN cscart_product_descriptions as descr1 ON descr1.product_id = products.product_id 
  AND descr1.lang_code = 'en' 
  LEFT JOIN cscart_product_prices as prices ON prices.product_id = products.product_id 
  AND prices.lower_limit = 1 
  INNER JOIN cscart_products_categories as products_categories ON products_categories.product_id = products.product_id 
  INNER JOIN cscart_categories ON cscart_categories.category_id = products_categories.category_id 
  LEFT JOIN cscart_supplier_links ON cscart_supplier_links.object_id = products.product_id 
  AND cscart_supplier_links.object_type = 'P' 
WHERE 
  1 
  AND prices.usergroup_id IN (0) 
  AND (
    (
      1 
      AND products.product_id IN (66837)
    ) 
    AND prices.usergroup_id IN (0)
  )

Query time 0.00041

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "1.67"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "products",
          "access_type": "const",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "product_id"
          ],
          "key_length": "3",
          "ref": [
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 1,
          "filtered": "100.00",
          "using_index": true,
          "cost_info": {
            "read_cost": "0.00",
            "eval_cost": "0.10",
            "prefix_cost": "0.00",
            "data_read_per_join": "5K"
          },
          "used_columns": [
            "product_id"
          ]
        }
      },
      {
        "table": {
          "table_name": "descr1",
          "access_type": "const",
          "possible_keys": [
            "PRIMARY",
            "product_id"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "product_id",
            "lang_code"
          ],
          "key_length": "9",
          "ref": [
            "const",
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 1,
          "filtered": "100.00",
          "using_index": true,
          "cost_info": {
            "read_cost": "0.00",
            "eval_cost": "0.10",
            "prefix_cost": "0.00",
            "data_read_per_join": "4K"
          },
          "used_columns": [
            "product_id",
            "lang_code"
          ]
        }
      },
      {
        "table": {
          "table_name": "prices",
          "access_type": "const",
          "possible_keys": [
            "usergroup",
            "product_id",
            "lower_limit",
            "usergroup_id",
            "idx_product_prices_usergroup_limit"
          ],
          "key": "usergroup",
          "used_key_parts": [
            "product_id",
            "usergroup_id",
            "lower_limit"
          ],
          "key_length": "9",
          "ref": [
            "const",
            "const",
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 1,
          "filtered": "100.00",
          "using_index": true,
          "cost_info": {
            "read_cost": "0.00",
            "eval_cost": "0.10",
            "prefix_cost": "0.00",
            "data_read_per_join": "24"
          },
          "used_columns": [
            "product_id",
            "lower_limit",
            "usergroup_id"
          ]
        }
      },
      {
        "table": {
          "table_name": "cscart_supplier_links",
          "access_type": "ref",
          "possible_keys": [
            "object_id"
          ],
          "key": "object_id",
          "used_key_parts": [
            "object_id",
            "object_type"
          ],
          "key_length": "7",
          "ref": [
            "const",
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 1,
          "filtered": "100.00",
          "using_index": true,
          "cost_info": {
            "read_cost": "0.25",
            "eval_cost": "0.10",
            "prefix_cost": "0.35",
            "data_read_per_join": "16"
          },
          "used_columns": [
            "object_id",
            "object_type"
          ]
        }
      },
      {
        "table": {
          "table_name": "products_categories",
          "access_type": "ref",
          "possible_keys": [
            "PRIMARY",
            "pt"
          ],
          "key": "pt",
          "used_key_parts": [
            "product_id"
          ],
          "key_length": "3",
          "ref": [
            "const"
          ],
          "rows_examined_per_scan": 2,
          "rows_produced_per_join": 2,
          "filtered": "100.00",
          "using_index": true,
          "cost_info": {
            "read_cost": "0.43",
            "eval_cost": "0.20",
            "prefix_cost": "0.98",
            "data_read_per_join": "32"
          },
          "used_columns": [
            "product_id",
            "category_id"
          ]
        }
      },
      {
        "table": {
          "table_name": "cscart_categories",
          "access_type": "eq_ref",
          "possible_keys": [
            "PRIMARY",
            "p_category_id"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "category_id"
          ],
          "key_length": "3",
          "ref": [
            "cscart_db.products_categories.category_id"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 2,
          "filtered": "100.00",
          "using_index": true,
          "cost_info": {
            "read_cost": "0.50",
            "eval_cost": "0.20",
            "prefix_cost": "1.68",
            "data_read_per_join": "5K"
          },
          "used_columns": [
            "category_id"
          ]
        }
      }
    ]
  }
}