我正在寻找一种方法,为我在Postgres中所有的表找到行数。我知道我可以一次做一张表:

SELECT count(*) FROM table_name;

但我想看看所有表的行数,然后按它排序,以了解所有表的大小。


当前回答

有三种方法可以得到这种计数,每种方法都有各自的权衡。

If you want a true count, you have to execute the SELECT statement like the one you used against each table. This is because PostgreSQL keeps row visibility information in the row itself, not anywhere else, so any accurate count can only be relative to some transaction. You're getting a count of what that transaction sees at the point in time when it executes. You could automate this to run against every table in the database, but you probably don't need that level of accuracy or want to wait that long.

WITH tbl AS
  (SELECT table_schema,
          TABLE_NAME
   FROM information_schema.tables
   WHERE TABLE_NAME not like 'pg_%'
     AND table_schema in ('public'))
SELECT table_schema,
       TABLE_NAME,
       (xpath('/row/c/text()', query_to_xml(format('select count(*) as c from %I.%I', table_schema, TABLE_NAME), FALSE, TRUE, '')))[1]::text::int AS rows_n
FROM tbl
ORDER BY rows_n DESC;

第二种方法指出,统计信息收集器在任何时候大致跟踪有多少行是“活动的”(没有被后来的更新删除或废弃)。这个值在剧烈活动时可能会偏离一点,但通常是一个很好的估计:

SELECT schemaname,relname,n_live_tup 
  FROM pg_stat_user_tables 
ORDER BY n_live_tup DESC;

这还可以显示有多少行已死,这本身就是一个值得监视的有趣数字。

第三种方法是注意到系统ANALYZE命令,从PostgreSQL 8.3开始由autovacuum进程定期执行以更新表统计信息,它也计算行估计。你可以像这样抓取它:

SELECT 
  nspname AS schemaname,relname,reltuples
FROM pg_class C
LEFT JOIN pg_namespace N ON (N.oid = C.relnamespace)
WHERE 
  nspname NOT IN ('pg_catalog', 'information_schema') AND
  relkind='r' 
ORDER BY reltuples DESC;

很难说使用这些查询中哪一个更好。通常,我根据是否有更多有用的信息也想在pg_class中使用,还是在pg_stat_user_tables中使用来做出决定。出于基本的计数目的,只是为了了解事物的总体大小,这两种方法都应该足够准确。

其他回答

我想从所有表的总数+表的列表与他们的计数。有点像绩效表,显示大部分时间都花在了哪里

WITH results AS ( 
  SELECT nspname AS schemaname,relname,reltuples
    FROM pg_class C
    LEFT JOIN pg_namespace N ON (N.oid = C.relnamespace)
    WHERE 
      nspname NOT IN ('pg_catalog', 'information_schema') AND
      relkind='r'
     GROUP BY schemaname, relname, reltuples
)

SELECT * FROM results
UNION
SELECT 'all' AS schemaname, 'all' AS relname, SUM(reltuples) AS "reltuples" FROM results

ORDER BY reltuples DESC

当然,你也可以在这个版本的结果上加上一个LIMIT条款,这样你就可以得到最大的n个违例者以及总数。

需要注意的一点是,在大量进口后,您需要让它静置一段时间。我通过跨几个表向数据库中添加5000行(使用实际导入数据)来测试这一点。它显示了大约一分钟的1800条记录(可能是一个可配置的窗口)

这是基于https://stackoverflow.com/a/2611745/1548557的工作,所以感谢并认可在CTE中使用的查询

我喜欢Daniel Vérité的回答。 但是当你不能使用CREATE语句时,你可以使用bash解决方案,如果你是windows用户,可以使用powershell解决方案:

# You don't need this if you have pgpass.conf
$env:PGPASSWORD = "userpass"

# Get table list
$tables = & 'C:\Program Files\PostgreSQL\9.4\bin\psql.exe' -U user -w -d dbname -At -c "select table_name from information_schema.tables where table_type='BASE TABLE' AND table_schema='schema1'"

foreach ($table in $tables) {
    & 'C:\path_to_postresql\bin\psql.exe' -U root -w -d dbname -At -c "select '$table', count(*) from $table"
}

有三种方法可以得到这种计数,每种方法都有各自的权衡。

If you want a true count, you have to execute the SELECT statement like the one you used against each table. This is because PostgreSQL keeps row visibility information in the row itself, not anywhere else, so any accurate count can only be relative to some transaction. You're getting a count of what that transaction sees at the point in time when it executes. You could automate this to run against every table in the database, but you probably don't need that level of accuracy or want to wait that long.

WITH tbl AS
  (SELECT table_schema,
          TABLE_NAME
   FROM information_schema.tables
   WHERE TABLE_NAME not like 'pg_%'
     AND table_schema in ('public'))
SELECT table_schema,
       TABLE_NAME,
       (xpath('/row/c/text()', query_to_xml(format('select count(*) as c from %I.%I', table_schema, TABLE_NAME), FALSE, TRUE, '')))[1]::text::int AS rows_n
FROM tbl
ORDER BY rows_n DESC;

第二种方法指出,统计信息收集器在任何时候大致跟踪有多少行是“活动的”(没有被后来的更新删除或废弃)。这个值在剧烈活动时可能会偏离一点,但通常是一个很好的估计:

SELECT schemaname,relname,n_live_tup 
  FROM pg_stat_user_tables 
ORDER BY n_live_tup DESC;

这还可以显示有多少行已死,这本身就是一个值得监视的有趣数字。

第三种方法是注意到系统ANALYZE命令,从PostgreSQL 8.3开始由autovacuum进程定期执行以更新表统计信息,它也计算行估计。你可以像这样抓取它:

SELECT 
  nspname AS schemaname,relname,reltuples
FROM pg_class C
LEFT JOIN pg_namespace N ON (N.oid = C.relnamespace)
WHERE 
  nspname NOT IN ('pg_catalog', 'information_schema') AND
  relkind='r' 
ORDER BY reltuples DESC;

很难说使用这些查询中哪一个更好。通常,我根据是否有更多有用的信息也想在pg_class中使用,还是在pg_stat_user_tables中使用来做出决定。出于基本的计数目的,只是为了了解事物的总体大小,这两种方法都应该足够准确。

摘自我在GregSmith的回答中的评论,使其更具可读性:

with tbl as (
  SELECT table_schema,table_name 
  FROM information_schema.tables
  WHERE table_name not like 'pg_%' AND table_schema IN ('public')
)
SELECT 
  table_schema, 
  table_name, 
  (xpath('/row/c/text()', 
    query_to_xml(format('select count(*) AS c from %I.%I', table_schema, table_name), 
    false, 
    true, 
    '')))[1]::text::int AS rows_n 
FROM tbl ORDER BY 3 DESC;

感谢@ a_horis_with_no_name

不确定bash中的答案对您来说是否可以接受,但FWIW…

PGCOMMAND=" psql -h localhost -U fred -d mydb -At -c \"
            SELECT   table_name
            FROM     information_schema.tables
            WHERE    table_type='BASE TABLE'
            AND      table_schema='public'
            \""
TABLENAMES=$(export PGPASSWORD=test; eval "$PGCOMMAND")

for TABLENAME in $TABLENAMES; do
    PGCOMMAND=" psql -h localhost -U fred -d mydb -At -c \"
                SELECT   '$TABLENAME',
                         count(*) 
                FROM     $TABLENAME
                \""
    eval "$PGCOMMAND"
done