我在许多wordpress网站上工作，这些网站的主题都是相同的。world.smart-shopping.com（db=54,9个月）et mes-bons-plans.be（db=14,6个月）。每个站点上的相同请求不会占用相同的时间。对于.be，大约是0,2秒，对于世界，大约是5秒。
这是（对世界）的要求：

SELECT SQL_CALC_FOUND_ROWS wpsmcp_posts.ID 
FROM wpsmcp_posts INNER
JOIN wpsmcp_postmeta ON ( wpsmcp_posts.ID = wpsmcp_postmeta.post_id )
INNER JOIN wpsmcp_postmeta AS mt1 ON ( wpsmcp_posts.ID = mt1.post_id )
WHERE 1=1 AND ( wpsmcp_postmeta.meta_key = '_wpc_expires' AND ( (
mt1.meta_key = '_wpc_expires' AND CAST(mt1.meta_value AS SIGNED)
BETWEEN '1546946077' AND '1547205277' ) ) ) AND wpsmcp_posts.post_type
= 'coupon' AND (wpsmcp_posts.post_status = 'publish' OR wpsmcp_posts.post_status = 'private') GROUP BY wpsmcp_posts.ID ORDER
BY wpsmcp_postmeta.meta_value+0 ASC LIMIT 0, 6

我运行了sql解释，但我在mysql中的水平太低，无法理解所有的事情。
对于。be：

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "38629.34"
    },
    "ordering_operation": {
      "using_filesort": true,
      "grouping_operation": {
        "using_temporary_table": true,
        "using_filesort": false,
        "nested_loop": [
          {
            "table": {
              "table_name": "wpsmbe_postmeta",
              "access_type": "ref",
              "possible_keys": [
                "post_id",
                "meta_key"
              ],
              "key": "meta_key",
              "used_key_parts": [
                "meta_key"
              ],
              "key_length": "767",
              "ref": [
                "const"
              ],
              "rows_examined_per_scan": 10433,
              "rows_produced_per_join": 10433,
              "filtered": "100.00",
              "cost_info": {
                "read_cost": "6075.00",
                "eval_cost": "2086.60",
                "prefix_cost": "8161.60",
                "data_read_per_join": "10M"
              },
              "used_columns": [
                "post_id",
                "meta_key",
                "meta_value"
              ],
              "attached_condition": "((`*_wpsmbe`.`wpsmbe_postmeta`.`meta_key` <=> '_wpc_expires') and (`*_wpsmbe`.`wpsmbe_postmeta`.`meta_key` = '_wpc_expires'))"
            }
          },
          {
            "table": {
              "table_name": "wpsmbe_posts",
              "access_type": "eq_ref",
              "possible_keys": [
                "PRIMARY",
                "type_status_date"
              ],
              "key": "PRIMARY",
              "used_key_parts": [
                "ID"
              ],
              "key_length": "8",
              "ref": [
                "*_wpsmbe.wpsmbe_postmeta.post_id"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 1150,
              "filtered": "11.03",
              "cost_info": {
                "read_cost": "10433.00",
                "eval_cost": "230.10",
                "prefix_cost": "20681.20",
                "data_read_per_join": "4M"
              },
              "used_columns": [
                "ID",
                "post_status",
                "post_type"
              ],
              "attached_condition": "((`*_wpsmbe`.`wpsmbe_posts`.`post_type` = 'coupon') and (`*_wpsmbe`.`wpsmbe_posts`.`post_status` = 'publish'))"
            }
          },
          {
            "table": {
              "table_name": "mt1",
              "access_type": "ref",
              "possible_keys": [
                "post_id",
                "meta_key"
              ],
              "key": "post_id",
              "used_key_parts": [
                "post_id"
              ],
              "key_length": "8",
              "ref": [
                "*_wpsmbe.wpsmbe_postmeta.post_id"
              ],
              "rows_examined_per_scan": 13,
              "rows_produced_per_join": 1044,
              "filtered": "6.99",
              "cost_info": {
                "read_cost": "14956.78",
                "eval_cost": "208.95",
                "prefix_cost": "38629.34",
                "data_read_per_join": "1M"
              },
              "used_columns": [
                "post_id",
                "meta_key",
                "meta_value"
              ],
              "attached_condition": "((`*_wpsmbe`.`mt1`.`meta_key` = '_wpc_expires') and (cast(`*_wpsmbe`.`mt1`.`meta_value` as signed) between '1547029897' and '1547289097'))"
            }
          }
        ]
      }
    }
  }
}

对于世界：

{
  "query_block": {
    "select_id": 1,
    "cost_info": {
      "query_cost": "439929.51"
    },
    "ordering_operation": {
      "using_filesort": true,
      "grouping_operation": {
        "using_temporary_table": true,
        "using_filesort": false,
        "nested_loop": [
          {
            "table": {
              "table_name": "wpsmcp_postmeta",
              "access_type": "ref",
              "possible_keys": [
                "post_id",
                "meta_key"
              ],
              "key": "meta_key",
              "used_key_parts": [
                "meta_key"
              ],
              "key_length": "767",
              "ref": [
                "const"
              ],
              "rows_examined_per_scan": 34921,
              "rows_produced_per_join": 34921,
              "filtered": "100.00",
              "cost_info": {
                "read_cost": "24303.00",
                "eval_cost": "6984.20",
                "prefix_cost": "31287.20",
                "data_read_per_join": "35M"
              },
              "used_columns": [
                "post_id",
                "meta_key",
                "meta_value"
              ],
              "attached_condition": "((`*_wpsmcp`.`wpsmcp_postmeta`.`meta_key` <=> '_wpc_expires') and (`*_wpsmcp`.`wpsmcp_postmeta`.`meta_key` = '_wpc_expires'))"
            }
          },
          {
            "table": {
              "table_name": "wpsmcp_posts",
              "access_type": "eq_ref",
              "possible_keys": [
                "PRIMARY",
                "type_status_date"
              ],
              "key": "PRIMARY",
              "used_key_parts": [
                "ID"
              ],
              "key_length": "8",
              "ref": [
                "*_wpsmcp.wpsmcp_postmeta.post_id"
              ],
              "rows_examined_per_scan": 1,
              "rows_produced_per_join": 27783,
              "filtered": "79.56",
              "cost_info": {
                "read_cost": "34921.00",
                "eval_cost": "5556.62",
                "prefix_cost": "73192.40",
                "data_read_per_join": "97M"
              },
              "used_columns": [
                "ID",
                "post_status",
                "post_type"
              ],
              "attached_condition": "((`*_wpsmcp`.`wpsmcp_posts`.`post_type` = 'coupon') and ((`*_wpsmcp`.`wpsmcp_posts`.`post_status` = 'publish') or (`*_wpsmcp`.`wpsmcp_posts`.`post_status` = 'private')))"
            }
          },
          {
            "table": {
              "table_name": "mt1",
              "access_type": "ref",
              "possible_keys": [
                "post_id",
                "meta_key"
              ],
              "key": "post_id",
              "used_key_parts": [
                "post_id"
              ],
              "key_length": "8",
              "ref": [
                "*_wpsmcp.wpsmcp_postmeta.post_id"
              ],
              "rows_examined_per_scan": 11,
              "rows_produced_per_join": 24298,
              "filtered": "7.95",
              "cost_info": {
                "read_cost": "305614.26",
                "eval_cost": "4859.76",
                "prefix_cost": "439929.51",
                "data_read_per_join": "24M"
              },
              "used_columns": [
                "post_id",
                "meta_key",
                "meta_value"
              ],
              "attached_condition": "((`*_wpsmcp`.`mt1`.`meta_key` = '_wpc_expires') and (cast(`*_wpsmcp`.`mt1`.`meta_value` as signed) between '1547025281' and '1547284481'))"
            }
          }
        ]
      }
    }
  }
}

你能帮我了解这些信息吗？我必须添加索引吗？或者别的什么？
谢谢