Details
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Type:
Task
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Status: Open
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Priority:
Minor
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Resolution: Unresolved
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Fix Version/s: None
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Component/s: Virtual Columns
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Labels:
Description
From the manual I can find out that:
There are two types of virtual , or computed, columns: PERSISTENT, which are stored in the table, and VIRTUAL, which are generated when the table is queried.
Why PERSISTENT column is Computed when it is stored in the table?
DROP TABLE IF EXISTS `raw__categories`;
create table `raw__categories` (
`id` BINARY(32) as (md5(CONCAT_WS('~',`ID_CATEGORY`,`ID_LANG`))) PERSISTENT,
`ID_CATEGORY` varchar(29) NOT NULL,
`ID_LANG` varchar(2) NOT NULL,
`NAME` varchar(40) NOT NULL,
PRIMARY KEY(`id`)
)
engine=InnoDB CHARSET=utf8;
I have an error:
#1903 - Primary key cannot be defined upon a computed column
It would be very useful to set up an ID algorithm using DDL
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If you wish, we can treat this report as a feature request.
Yes, It would be great.
Thank you.
Because it is computed; as per the general definition, "its value automatically calculated using a deterministic expression, in particular from the values of other fields in the table".
The difference is when it's calculated – upon storing or upon retrieval.
The fact that primary keys are not supported is also explicitly documented here: https://mariadb.com/kb/en/mariadb/virtual-computed-columns/.
If you wish, we can treat this report as a feature request.