Postgres knex query joining columns - sql

Question

I have a Postgres DB that stores data in a table that has the following columns "date | uid | id | value | data".
Using knex on a node.js server I currently get from this query:
data = await db(tableName).select(["date", "uid", "id", "value", "value as market_cap", "data"]).whereIn("id", ["index", "market_cap", "market"]);
the following result:
"data": [
{
"date": "2020-11-07T21:43:11.709Z",
"uid": "nmvdqy0kh87sd8a",
"id": "index",
"value": "999.9999999999999",
"market_cap": "999.9999999999999",
"data": null
},
{
"date": "2020-11-07T21:43:11.709Z",
"uid": "nmvdqy0kh87sd8b",
"id": "market_cap",
"value": "10125616413",
"market_cap": "10125616413",
"data": null
},
{
"date": "2020-11-07T21:43:11.709Z",
"uid": "nmvdqy0kh87sd8c",
"id": "market",
"value": null,
"market_cap": null,
"data": {
"1": [],
"2": []
}
},
...
];
The date pairs are all exactly the same. Data stored under id "market_cap" is actually stored as "value" and data stored under id "market" is actually stored as "data".
Now, what I actually need is:
"data": [
{
"date": "2020-11-07T21:43:11.709Z",
"value": "999.9999999999999",
"market_cap": "10125616413",
"data": {
"1": [],
"2": []
}
},
...
];
Is there a way to obtain this data structure directly from the database instead of transforming the data on the server? Bonus points it you provide the knex query / SQL query. Thank you!

Answer 1

You can accomplish this with a self-join on date and selecting on the rows with certain IDs. Left join ensures a result for each date even if they're missing a data type.
select mv."date", mv.value, mc.value as market_cap, md.data
from market_snapshots mv
left join market_snapshots mc on mv."date" = mc."date" and mc.id = 'market_cap'
left join market_snapshots md on mv."date" = md."date" and md.id = 'market'
where mv.id = 'index';
Try it.
In Knex it would be something like...
knex.select(['mv.date', 'mv.value', 'mc.value as market_cap', 'md.data'])
.from({ mv: 'market_snapshots' })
.leftJoin({ mc: 'market_snapshots' }, function() {
this.on('mv.date', '=', 'mc.date').andOn(knex.raw('mc.id = ?', 'market_cap'))
})
.leftJoin({ md: 'market_snapshots' }, function() {
this.on('mv.date', '=', 'md.date').andOn(knex.raw('md.id = ?', 'market'))
})
.where('mv.id', 'index')