Consider:
CREATE TABLE testwid
(
txtnotnull text,
txtnull text,
int8notnull int8,
int8null int8
);
INSERT INTO testwid
SELECT 'a' || g.i,
NULL,
g.i,
NULL
FROM generate_series(1,10000) AS g(i);
ANALYZE testwid;
SELECT attname, avg_width FROM pg_stats WHERE tablename = 'testwid';
attname | avg_width
-------------+-----------
txtnotnull | 5
txtnull | 0
int8notnull | 8
int8null | 8
(4 rows)
I see in analyze.c
8<-----------------
/* We can only compute average width if we found some non-null values.*/
if (nonnull_cnt > 0)
[snip]
else if (null_cnt > 0)
{
/* We found only nulls; assume the column is entirely null */
stats->stats_valid = true;
stats->stanullfrac = 1.0;
if (is_varwidth)
stats->stawidth = 0; /* "unknown" */
else
stats->stawidth = stats->attrtype->typlen;
stats->stadistinct = 0.0; /* "unknown" */
}
8<-----------------
So apparently intentional, but seems gratuitously inconsistent. Could
this cause any actual inconsistent behaviors? In any case that first
comment does not reflect the code.
Joe
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