What does `NUMERIC maxsize 256` mean in mysql? - mysql

Question

Here is a data fields definition:
Field Name
Field Description
Field Type (format)
Max Size
May be NULL
Key
tag
The unique identifier (name) for a tag in a specific taxonomy release.
ALPHANUMERIC
256
No
*
version
For a standard tag, an identifier for the taxonomy; otherwise the accession number where the tag was defined.
ALPHANUMERIC
20
No
*
ddate
The end date for the data value, rounded to the nearest month end.
DATE (yyyymmdd)
8
No
*
qtrs
The count of the number of quarters represented by the data value, rounded to the nearest whole number. “0” indicates it is a point-in-time value.
NUMERIC
8
No
*
uom
The unit of measure for the value.
ALPHANUMERIC
20
No
*
coreg
If specified, indicates a specific co-registrant, the parent company, or other entity (e.g., guarantor).  NULL indicates the consolidated entity.
NUMERIC
256
Yes
*
value
The value. This is not scaled, it is as found in the Interactive Data file, but is limited to four digits to the right of the decimal point.
NUMERIC(28,4)
16
Yes
footnote
The text of any superscripted footnotes on the value, as shown on the statement page, truncated to 512 characters, or if there is no footnote, then this field will be blank.
ALPHANUMERIC
512
Yes
The field definition is SEC U.S. Securities and Exchange Commission's official material:
sec official material
For coreg ,it's field type is numeric ,max size 256 ,how to write the create statement?
CREATE TABLE `num` (
`id` INT NOT NULL AUTO_INCREMENT,
`tag` VARCHAR(256) NOT NULL,
`version` VARCHAR(20) NOT NULL,
`ddate` DATE NOT NULL,
`qtrs` DECIMAL(8) NOT NULL,
`uom` VARCHAR(20) NOT NULL,
`coreg` ?,
`value` DECIMAL(28,4),
`footnote` VARCHAR(512),
PRIMARY KEY (id)
);
To write the field definiton as below?
`coreg` NUMERIC(256)

Answer 1

In MySQL the maximum number of digits for decimal (numeric) type is 65.
So, you can't technically define a column as NUMERIC(256).
11.1.3 Fixed-Point Types (Exact Value) - DECIMAL, NUMERIC
The maximum number of digits for DECIMAL is 65
It doesn't really make sense to me to have the "the parent company, or other entity (e.g., guarantor)" defined as a number, even as a really long number.
Maybe there is a typo and really it should read "ALPHANUMERIC", i.e. a text value.
If this value will never be interpreted as a number and there will never be attempts to make some calculations with this number (as the field description implies), then it should be stored as a text (varchar(256)); maybe with some extra checks that you can store only digits 0-9 and not any symbol there.

Answer 2

It probably means it's just a long sequence of digits. You would typically store it as a NUMERIC but a size of 256 digits is beyond MySQL's limit for numeric types. You can store it, however, as a VARCHAR(256) and add a CHECK constraint on it.
Note: CHECK constraints are enforced only in MySQL 8.0 (8.0.3?) and newer.
For example:
create table t (
coreg varchar(256) check (coreg regexp '^[0-9]+$')
);
insert into t (coreg) values ('123');
insert into t (coreg) values ('x456'); -- fails
insert into t (coreg) values ('7y89'); -- fails
insert into t (coreg) values ('012z'); -- fails
insert into t (coreg) values ('345 '); -- fails
See running example in db<>fiddle.