PostgreSQL + ANALYZE + pg_statistic表

Question

我有關於pg_statistic表的問題，它存儲來自ANALYZE的數據。有人能告訴我這張表的列是什麼？我有名單here，但我不知道（不明白）這一列是什麼：stanullfrac,stadistinct,stakindN,staopN,stanumbersN,stavaluesN。

Answer 1

對我來說似乎很簡單。特別是如果你看看裏面定義的更人性化pg_stat視圖（\d+ pg_stats）

例如，說：使用

select * from pg_statistic where starelid = 23825 and staattnum=2; 

starelid | 23825  => table (oid) 
staattnum | 2   => column 2 
stanullfrac | 0   => 0% null valuess 
stadistinct | -0.484307 => about 48% are distict, i.e., the average repetition is about 2 
stakind1 | 1     => code '1' : most common vals 
stavalues1 | {"John","Mary" ... => values of most common valss 
stanumbers1 | {0.0086,0.0064 ... => percentage occurrence of common vals 
stakind2 | 2     => code '2' : histogram bounds 
stavalues2 | {-,"AAA", ...  => values (bounds) for histogram intervals 
stanumbers2 | 
stakind3 | 3     => code '3' => correlation 
stavalues3 | 
stanumbers3 | {0.00826469}  => correlation coefficient 

同樣的事情human_readable pg_stats觀點：

select * from pg_stats where tablename = 'persons' and attname = 'first_name'; 
schemaname  | public 
tablename   | persons 
attname   | first_name 
inherited   | f 
null_frac   | 0 
avg_width   | 11 
n_distinct  | -0.484307 
most_common_vals | {"John","Mary"... 
most_common_freqs | {0.00867898,0.00640832... 
histogram_bounds | {-,"AAA"... 
correlation  | 0.00826469