Is it possible to create a PERSISTED column that's made up of an array of specific JSON values and if so how? - singlestore

Question

Is it possible to create a PERSISTED column that's made up of an array of specific JSON values and if so how?
Simple Example (json column named data):
{ name: "Jerry", age: 91, mother: "Janet", father: "Eustace" }
Persisted Column Hopeful (assuming json column is called 'data'):
ALTER TABLE tablename ADD parents [ data::$mother, data::$father ] AS PERSISTED JSON;
Expected Output
| data (json) | parents (persisted json) |
| -------------------------------------------------------------- | ------------------------- |
| { name: "Jerry", age: 91, mother: "Janet", father: "Eustace" } | [ "Janet", "Eustace" ] |
| { name: "Eustace", age: 106, mother: "Jane" } | [ "Jane" ] |
| { name: "Jim", age: 54, mother: "Rachael", father: "Dom" } | [ "Rachael", "Dom ] |
| -------------------------------------------------------------- | ------------------------- |
The above doesn't work, but hopefully it conveys what I'm trying to accomplish.

Answer 1

There is no PERSISTED ARRAY data type for columns, but there is a JSON column type that can store arrays.
For example:
-- The existing table
create table tablename (
id int primary key AUTO_INCREMENT
);
-- Add the new JSON column
ALTER TABLE tablename ADD column parents JSON;
-- Insert data into the table
INSERT INTO tablename (parents) VALUES
('[ "Janet", "Eustace" ]'),
('[ "Jane" ]');
-- Select table based on matches in the JSON column
select *
from tablename
where JSON_ARRAY_CONTAINS_STRING(parents, 'Jane');
-- Change data in the JSON column
update tablename
set parents = JSON_ARRAY_PUSH_STRING(parents, 'Jon')
where JSON_ARRAY_CONTAINS_STRING(parents, 'Jane')
-- Show changed data
select *
from tablename
where JSON_ARRAY_CONTAINS_STRING(parents, 'Jane');
Check out more examples of pushing and selecting JSON data in the docs at https://docs.memsql.com/v7.0/concepts/json-guide/

Answer 2

Here is a sample table definition where I do something similar with customer and event:
CREATE TABLE `eventsext2` (
`data` JSON COLLATE utf8_bin DEFAULT NULL,
`memsql_insert_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP,
`customer` as data::$custID PERSISTED text CHARACTER SET utf8 COLLATE utf8_general_ci,
`event` as data::$event PERSISTED text CHARACTER SET utf8 COLLATE utf8_general_ci,
customerevent as concat(data::$custID,", ",data::$event) persisted text,
`generator` as data::$genID PERSISTED text CHARACTER SET utf8 COLLATE utf8_general_ci,
`latitude` as (substr(data::$longlat from (instr(data::$longlat,'|')+1))) PERSISTED decimal(21,18),
`longitude` as (substr(data::$longlat from 1 for (instr(data::$longlat,'|')-1))) PERSISTED decimal(21,18),
`location` as concat('POINT(',latitude,' ',longitude,')') PERSISTED geographypoint,
KEY `memsql_insert_time` (`memsql_insert_time`)
/*!90618 , SHARD KEY () */
) /*!90623 AUTOSTATS_CARDINALITY_MODE=OFF, AUTOSTATS_HISTOGRAM_MODE=OFF */ /*!90623 SQL_MODE='STRICT_ALL_TABLES' */;

Answer 3

Though not your question, denormalizing this table into two tables might be a good choice:
create table parents (
id int primary key auto_increment,
tablenameid int not null,
name varchar(20),
type int not null, -- 1=Father, 2=Mother, ideally foreign key to other table
);