Gorm decimal precision - Nineya|java/go/python

update := map[string]interface{}{ "field1": gorm.Expr("field1 + (?)", changes.Field1), "field2": gorm.Expr("field2 + (?)", changes.Field2), "field3": gorm.Expr("field3 + (?)", changes.Field3), }

The type of fields 1~3 is decimal.Decimal. When updating mysql with the update map for about hunderds of times, the decimal precision will be lost, like 3.3689999999999998.

MySQL [example]> CREATE TABLE demo ( -> id int not null primary key, -> amount decimal(27,18) not null -> ); Query OK, 0 rows affected (0.238 sec)

MySQL [example]> INSERT INTO demo values (1, 0); Query OK, 1 row affected (0.215 sec)

MySQL [example]> select * from demo; +----+----------------------+ | id | amount | +----+----------------------+ | 1 | 0.000000000000000000 | +----+----------------------+ 1 row in set (0.216 sec)

MySQL [example]> UPDATE demo SET amount = amount + '1.123'; Query OK, 1 row affected (0.219 sec) Rows matched: 1 Changed: 1 Warnings: 0

MySQL [example]> select * from demo; +----+----------------------+ | id | amount | +----+----------------------+ | 1 | 1.123000000000000000 | +----+----------------------+ 1 row in set (0.266 sec)

MySQL [example]> UPDATE demo SET amount = amount + '1.123'; Query OK, 1 row affected (0.235 sec) Rows matched: 1 Changed: 1 Warnings: 0

MySQL [example]> select * from demo; +----+----------------------+ | id | amount | +----+----------------------+ | 1 | 2.246000000000000000 | +----+----------------------+ 1 row in set (0.270 sec)

MySQL [example]> UPDATE demo SET amount = amount + '1.123'; Query OK, 1 row affected (0.417 sec) Rows matched: 1 Changed: 1 Warnings: 0

MySQL [example]> select * from demo; +----+----------------------+ | id | amount | +----+----------------------+ | 1 | 3.368999999999999800 | +----+----------------------+ 1 row in set (0.214 sec)

Comment From: github-actions[bot]

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Comment From: Heliner

it sounds like some future of mysql try this

CREATE TABLE demo (
 id int not null primary key,
 amount decimal(27,18) not null
);

INSERT INTO demo values (1, 0);
UPDATE demo SET amount = amount + 1.123;
select * from demo;

UPDATE demo SET amount = amount + 1.123;
select * from demo;

UPDATE demo SET amount = amount + 1.123;
select * from demo;

--id    amount
--1 1.123000000000000000
--id    amount
--1 2.246000000000000000
--id    amount
--1 3.369000000000000000

https://paiza.io/projects/lbp9qwjko_vk0oArQK00gw?language=mysql

Comment From: github-actions[bot]