SELECT 
  COUNT(
    DISTINCT(cscart_companies.company_id)
  ) 
FROM 
  cscart_companies 
  LEFT JOIN cscart_company_descriptions ON cscart_company_descriptions.company_id = cscart_companies.company_id 
  AND cscart_company_descriptions.lang_code = 'en' 
  LEFT JOIN cscart_vendor_plan_descriptions ON cscart_companies.plan_id = cscart_vendor_plan_descriptions.plan_id 
  AND cscart_vendor_plan_descriptions.lang_code = 'en' 
  LEFT JOIN cscart_seo_names ON cscart_seo_names.object_id = cscart_companies.company_id 
  AND cscart_seo_names.type = 'm' 
  AND cscart_seo_names.dispatch = '' 
  AND cscart_seo_names.lang_code = 'en' 
  LEFT JOIN cscart_discussion ON cscart_discussion.object_id = cscart_companies.company_id 
  AND cscart_discussion.object_type = 'M' 
  LEFT JOIN cscart_discussion_posts ON cscart_discussion_posts.thread_id = cscart_discussion.thread_id 
  AND cscart_discussion_posts.status = 'A' 
  LEFT JOIN cscart_discussion_rating ON cscart_discussion.thread_id = cscart_discussion_rating.thread_id 
  AND cscart_discussion_rating.post_id = cscart_discussion_posts.post_id 
WHERE 
  1 
  AND cscart_companies.status IN ('A', 'S')

Query time 0.00083

JSON explain

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "0.45"
    },
    "nested_loop": [
      {
        "table": {
          "table_name": "cscart_companies",
          "access_type": "system",
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 1,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "0.00",
            "eval_cost": "0.10",
            "prefix_cost": "0.00",
            "data_read_per_join": "6K"
          },
          "used_columns": [
            "company_id",
            "status",
            "plan_id"
          ]
        }
      },
      {
        "table": {
          "table_name": "cscart_discussion_posts",
          "access_type": "system",
          "possible_keys": [
            "thread_id",
            "thread_id_2"
          ],
          "rows_examined_per_scan": 0,
          "rows_produced_per_join": 1,
          "filtered": "0.00",
          "const_row_not_found": true,
          "cost_info": {
            "read_cost": "0.00",
            "eval_cost": "0.10",
            "prefix_cost": "0.00",
            "data_read_per_join": "448"
          },
          "used_columns": [
            "post_id",
            "thread_id",
            "status"
          ]
        }
      },
      {
        "table": {
          "table_name": "cscart_discussion_rating",
          "access_type": "system",
          "possible_keys": [
            "PRIMARY",
            "thread_id"
          ],
          "rows_examined_per_scan": 0,
          "rows_produced_per_join": 1,
          "filtered": "0.00",
          "const_row_not_found": true,
          "cost_info": {
            "read_cost": "0.00",
            "eval_cost": "0.10",
            "prefix_cost": "0.00",
            "data_read_per_join": "16"
          },
          "used_columns": [
            "post_id",
            "thread_id"
          ]
        }
      },
      {
        "table": {
          "table_name": "cscart_company_descriptions",
          "access_type": "const",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "company_id",
            "lang_code"
          ],
          "key_length": "10",
          "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": "40"
          },
          "used_columns": [
            "company_id",
            "lang_code"
          ]
        }
      },
      {
        "table": {
          "table_name": "cscart_vendor_plan_descriptions",
          "access_type": "const",
          "possible_keys": [
            "PRIMARY"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "plan_id",
            "lang_code"
          ],
          "key_length": "10",
          "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": "792"
          },
          "used_columns": [
            "plan_id",
            "lang_code"
          ]
        }
      },
      {
        "table": {
          "table_name": "cscart_seo_names",
          "access_type": "ref",
          "possible_keys": [
            "PRIMARY",
            "dispatch"
          ],
          "key": "PRIMARY",
          "used_key_parts": [
            "object_id",
            "type",
            "dispatch",
            "lang_code"
          ],
          "key_length": "206",
          "ref": [
            "const",
            "const",
            "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": "1K"
          },
          "used_columns": [
            "object_id",
            "type",
            "dispatch",
            "lang_code"
          ],
          "attached_condition": "<if>(is_not_null_compl(cscart_seo_names), (`betaatif_store`.`cscart_seo_names`.`object_id` = '1'), true)"
        }
      },
      {
        "table": {
          "table_name": "cscart_discussion",
          "access_type": "const",
          "possible_keys": [
            "object_id"
          ],
          "key": "object_id",
          "used_key_parts": [
            "object_id",
            "object_type"
          ],
          "key_length": "6",
          "ref": [
            "const",
            "const"
          ],
          "rows_examined_per_scan": 1,
          "rows_produced_per_join": 1,
          "filtered": "100.00",
          "cost_info": {
            "read_cost": "0.00",
            "eval_cost": "0.10",
            "prefix_cost": "0.45",
            "data_read_per_join": "24"
          },
          "used_columns": [
            "thread_id",
            "object_id",
            "object_type"
          ],
          "attached_condition": "<if>(is_not_null_compl(cscart_discussion), (`betaatif_store`.`cscart_discussion`.`object_id` = '1'), true)"
        }
      }
    ]
  }
}