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Add documentation and regression tests concerning rounding of numerics. 

Michael Paquier, reviewed by Fabien Coelho
This commit is contained in:
Tom Lane 2015-07-03 17:04:39 -04:00
parent 8eb6407aae
commit 5e7c3d91bf
10 changed files with 169 additions and 0 deletions
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25
doc/src/sgml/datatype.sgml
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@ -612,6 +612,31 @@ NUMERIC
equivalent. Both types are part of the <acronym>SQL</acronym>
standard.
</para>
<para>
When rounding values, the <type>numeric</type> type rounds ties away
from zero, while (on most machines) the <type>real</type>
and <type>double precision</type> types round ties to the nearest even
number. For example:
<programlisting>
SELECT x,
round(x::numeric) AS num_round,
round(x::double precision) AS dbl_round
FROM generate_series(-3.5, 3.5, 1) as x;
x | num_round | dbl_round
------+-----------+-----------
-3.5 | -4 | -4
-2.5 | -3 | -2
-1.5 | -2 | -2
-0.5 | -1 | -0
0.5 | 1 | 0
1.5 | 2 | 2
2.5 | 3 | 2
3.5 | 4 | 4
(8 rows)
</programlisting>
</para>
</sect2>

20
src/test/regress/expected/int2.out
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@ -286,3 +286,23 @@ FROM (VALUES (-2.5::float8),
2.5 | 2
(7 rows)
-- check rounding when casting from numeric
SELECT x, x::int2 AS int2_value
FROM (VALUES (-2.5::numeric),
(-1.5::numeric),
(-0.5::numeric),
(0.0::numeric),
(0.5::numeric),
(1.5::numeric),
(2.5::numeric)) t(x);
x | int2_value
------+------------
-2.5 | -3
-1.5 | -2
-0.5 | -1
0.0 | 0
0.5 | 1
1.5 | 2
2.5 | 3
(7 rows)

20
src/test/regress/expected/int4.out
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@ -383,3 +383,23 @@ FROM (VALUES (-2.5::float8),
2.5 | 2
(7 rows)
-- check rounding when casting from numeric
SELECT x, x::int4 AS int4_value
FROM (VALUES (-2.5::numeric),
(-1.5::numeric),
(-0.5::numeric),
(0.0::numeric),
(0.5::numeric),
(1.5::numeric),
(2.5::numeric)) t(x);
x | int4_value
------+------------
-2.5 | -3
-1.5 | -2
-0.5 | -1
0.0 | 0
0.5 | 1
1.5 | 2
2.5 | 3
(7 rows)

20
src/test/regress/expected/int8-exp-three-digits.out
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@ -866,3 +866,23 @@ FROM (VALUES (-2.5::float8),
2.5 | 2
(7 rows)
-- check rounding when casting from numeric
SELECT x, x::int8 AS int8_value
FROM (VALUES (-2.5::numeric),
(-1.5::numeric),
(-0.5::numeric),
(0.0::numeric),
(0.5::numeric),
(1.5::numeric),
(2.5::numeric)) t(x);
x | int8_value
------+------------
-2.5 | -3
-1.5 | -2
-0.5 | -1
0.0 | 0
0.5 | 1
1.5 | 2
2.5 | 3
(7 rows)

20
src/test/regress/expected/int8.out
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@ -866,3 +866,23 @@ FROM (VALUES (-2.5::float8),
2.5 | 2
(7 rows)
-- check rounding when casting from numeric
SELECT x, x::int8 AS int8_value
FROM (VALUES (-2.5::numeric),
(-1.5::numeric),
(-0.5::numeric),
(0.0::numeric),
(0.5::numeric),
(1.5::numeric),
(2.5::numeric)) t(x);
x | int8_value
------+------------
-2.5 | -3
-1.5 | -2
-0.5 | -1
0.0 | 0
0.5 | 1
1.5 | 2
2.5 | 3
(7 rows)

24
src/test/regress/expected/numeric.out
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@ -730,6 +730,30 @@ SELECT a, ceil(a), ceiling(a), floor(a), round(a) FROM ceil_floor_round;
(7 rows)
DROP TABLE ceil_floor_round;
-- Check rounding, it should round ties away from zero.
SELECT i as pow,
round((-2.5 * 10 ^ i)::numeric, -i),
round((-1.5 * 10 ^ i)::numeric, -i),
round((-0.5 * 10 ^ i)::numeric, -i),
round((0.5 * 10 ^ i)::numeric, -i),
round((1.5 * 10 ^ i)::numeric, -i),
round((2.5 * 10 ^ i)::numeric, -i)
FROM generate_series(-5,5) AS t(i);
pow | round | round | round | round | round | round
-----+----------+----------+----------+---------+---------+---------
-5 | -0.00003 | -0.00002 | -0.00001 | 0.00001 | 0.00002 | 0.00003
-4 | -0.0003 | -0.0002 | -0.0001 | 0.0001 | 0.0002 | 0.0003
-3 | -0.003 | -0.002 | -0.001 | 0.001 | 0.002 | 0.003
-2 | -0.03 | -0.02 | -0.01 | 0.01 | 0.02 | 0.03
-1 | -0.3 | -0.2 | -0.1 | 0.1 | 0.2 | 0.3
0 | -3 | -2 | -1 | 1 | 2 | 3
1 | -30 | -20 | -10 | 10 | 20 | 30
2 | -300 | -200 | -100 | 100 | 200 | 300
3 | -3000 | -2000 | -1000 | 1000 | 2000 | 3000
4 | -30000 | -20000 | -10000 | 10000 | 20000 | 30000
5 | -300000 | -200000 | -100000 | 100000 | 200000 | 300000
(11 rows)
-- Testing for width_bucket(). For convenience, we test both the
-- numeric and float8 versions of the function in this file.
-- errors

10
src/test/regress/sql/int2.sql
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@ -102,3 +102,13 @@ FROM (VALUES (-2.5::float8),
(0.5::float8),
(1.5::float8),
(2.5::float8)) t(x);
-- check rounding when casting from numeric
SELECT x, x::int2 AS int2_value
FROM (VALUES (-2.5::numeric),
(-1.5::numeric),
(-0.5::numeric),
(0.0::numeric),
(0.5::numeric),
(1.5::numeric),
(2.5::numeric)) t(x);

10
src/test/regress/sql/int4.sql
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@ -145,3 +145,13 @@ FROM (VALUES (-2.5::float8),
(0.5::float8),
(1.5::float8),
(2.5::float8)) t(x);
-- check rounding when casting from numeric
SELECT x, x::int4 AS int4_value
FROM (VALUES (-2.5::numeric),
(-1.5::numeric),
(-0.5::numeric),
(0.0::numeric),
(0.5::numeric),
(1.5::numeric),
(2.5::numeric)) t(x);

10
src/test/regress/sql/int8.sql
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@ -215,3 +215,13 @@ FROM (VALUES (-2.5::float8),
(0.5::float8),
(1.5::float8),
(2.5::float8)) t(x);
-- check rounding when casting from numeric
SELECT x, x::int8 AS int8_value
FROM (VALUES (-2.5::numeric),
(-1.5::numeric),
(-0.5::numeric),
(0.0::numeric),
(0.5::numeric),
(1.5::numeric),
(2.5::numeric)) t(x);

10
src/test/regress/sql/numeric.sql
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@ -667,6 +667,16 @@ INSERT INTO ceil_floor_round VALUES ('-0.000001');
SELECT a, ceil(a), ceiling(a), floor(a), round(a) FROM ceil_floor_round;
DROP TABLE ceil_floor_round;
-- Check rounding, it should round ties away from zero.
SELECT i as pow,
round((-2.5 * 10 ^ i)::numeric, -i),
round((-1.5 * 10 ^ i)::numeric, -i),
round((-0.5 * 10 ^ i)::numeric, -i),
round((0.5 * 10 ^ i)::numeric, -i),
round((1.5 * 10 ^ i)::numeric, -i),
round((2.5 * 10 ^ i)::numeric, -i)
FROM generate_series(-5,5) AS t(i);
-- Testing for width_bucket(). For convenience, we test both the
-- numeric and float8 versions of the function in this file.