Обсуждение: [GENERAL] pg_column_size strange result...

Hi,

I was calculating row sizes with pg_column_size and came to this strange
result:

CREATE TABLE t1(
     c1 NUMERIC(10,7) NOT NULL DEFAULT 123.1234567
);

INSERT INTO t1(c1) VALUES (DEFAULT);

SELECT pg_column_size(c1) AS first,
pg_column_size(123.1234567::NUMERIC(10,7)) as second, c1 =
123.1234567::NUMERIC(10,7) AS are_equal
FROM t1;

+-------+--------+-----------+
| first | second | are_equal |
+-------+--------+-----------+
|     9 |     12 |         t |
+-------+--------+-----------+

Is there a reason pg_column_size returns different sizes for a constant
and the same value from a table column?

Regards,
Mladen Marinović

marin@kset.org writes:
> Is there a reason pg_column_size returns different sizes for a constant
> and the same value from a table column?

The constant probably has the default choice of a four-byte length word,
while the on-disk form has been compressed by switching to a one-byte
length word.

            regards, tom lane