Question

我使用以下查询查询表中所有记录的计数： -

groups=# select count(*) from auth_user;
  count
---------
 1000000
(1 row)

以下是上表的架构： -

groups=# \d auth_user;
                                     Table "public.auth_user"
    Column    |           Type           |                       Modifiers
--------------+--------------------------+--------------------------------------------------------
 id           | integer                  | not null default nextval('auth_user_id_seq'::regclass)
 password     | character varying(128)   | not null
 last_login   | timestamp with time zone |
 is_superuser | boolean                  | not null
 username     | character varying(150)   | not null
 first_name   | character varying(30)    | not null
 last_name    | character varying(150)   | not null
 email        | character varying(254)   | not null
 is_staff     | boolean                  | not null
 is_active    | boolean                  | not null
 date_joined  | timestamp with time zone | not null
Indexes:
    "auth_user_pkey" PRIMARY KEY, btree (id)
    "auth_user_username_key" UNIQUE CONSTRAINT, btree (username)
    "auth_user_username_6821ab7c_like" btree (username varchar_pattern_ops)
Referenced by:
    TABLE "auth_user_groups" CONSTRAINT "auth_user_groups_user_id_6a12ed8b_fk_auth_user_id" FOREIGN KEY (user_id) REFERENCES auth_user(id) DEFERRABLE INITIALLY DEFERRED
    TABLE "auth_user_user_permissions" CONSTRAINT "auth_user_user_permissions_user_id_a95ead1b_fk_auth_user_id" FOREIGN KEY (user_id) REFERENCES auth_user(id) DEFERRABLE INITIALLY DEFERRED
    TABLE "django_admin_log" CONSTRAINT "django_admin_log_user_id_c564eba6_fk" FOREIGN KEY (user_id) REFERENCES auth_user(id) DEFERRABLE INITIALLY DEFERRED
    TABLE "groups_membership" CONSTRAINT "groups_membership_approved_by_id_e04d19ff_fk_auth_user_id" FOREIGN KEY (approved_by_id) REFERENCES auth_user(id) DEFERRABLE INITIALLY DEFERRED
    TABLE "groups_membership" CONSTRAINT "groups_membership_member_id_241678d9_fk_auth_user_id" FOREIGN KEY (member_id) REFERENCES auth_user(id) DEFERRABLE INITIALLY DEFERRED
    TABLE "groups_membershipinvite" CONSTRAINT "groups_membershipinvite_receiver_id_f8261ed4_fk_auth_user_id" FOREIGN KEY (receiver_id) REFERENCES auth_user(id) DEFERRABLE INITIALLY DEFERRED
    TABLE "groups_membershipinvite" CONSTRAINT "groups_membershipinvite_sender_id_09bda548_fk_auth_user_id" FOREIGN KEY (sender_id) REFERENCES auth_user(id) DEFERRABLE INITIALLY DEFERRED
    TABLE "groups_membershiprequest" CONSTRAINT "groups_membershiprequest_requestor_id_23767f01_fk_auth_user_id" FOREIGN KEY (requestor_id) REFERENCES auth_user(id) DEFERRABLE INITIALLY DEFERRED

现在，当我使用explain来分析上面查询的执行计划时，显示的记录计数显示额外的80行

groups=# explain analyze  select count(*) from auth_user;
                                                         QUERY PLAN
----------------------------------------------------------------------------------------------------------------------------
 Aggregate  (cost=20835.00..20835.01 rows=1 width=0) (actual time=830.661..830.661 rows=1 loops=1)
   ->  Seq Scan on auth_user  (cost=0.00..18334.80 rows=1000080 width=0) (actual time=41.071..779.325 rows=1000000 loops=1)
 Planning time: 0.052 ms
 Execution time: 830.691 ms
(4 rows)

我的问题是，这80行来自哪里？我错过了什么吗？

提前致谢。

为什么postgres在analyze语句中显示的行数多于表中的实际行数？

0 个答案: