Create a hardcoded "mapping table" in Trino SQL - sql

Question

I have a query (several CTEs) that get data from different sources. The output has a column name, but I would like to map this nameg to a more user-friendly name.
Id
name
1
buy
2
send
3
paid
I would like to hard code somewhere in the query (in another CTE?) a mapping table. Don't want to create a separate table for it, just plain text.
name_map=[('buy', 'Item purchased'),('send', 'Parcel in transit'), ('paid', 'Charge processed')]
So output table would be:
Id
name
1
Item purchased
2
Parcel in transit
3
Charge processed
In Trino I see the function map_from_entries and element_at, but don't know if they could work in this case.
I know "case when" might work, but if possible, a mapping table would be more convenient.
Thanks

Answer 1

As a simpler alternative to the other answer, you don't actually need to create an intermediate map using map_from_entries and look up values using element_at. You can just create an inline mapping table with VALUES and use a regular JOIN to do the lookups:
WITH mapping(name, description) AS (
VALUES
('buy', 'Item purchased'),
('send', 'Parcel in transit'),
('paid', 'Charge processed')
)
SELECT description
FROM t JOIN mapping ON t.name = mapping.name
(The query assumes your data is in a table named t that contains a column named name to use for the lookup)

Answer 2

Super interesting idea, and I think I got it working:
with tmp as (
SELECT *
FROM (VALUES ('1', 'buy'),
('2', 'send'),
('3', 'paid')) as t(id, name)
)
SELECT element_at(name_map, name) as name
FROM tmp
JOIN (VALUES map_from_entries(
ARRAY[('buy', 'Item purchased'),
('send', 'Parcel in transit'),
('paid', 'Charge processed')])) as t(name_map) ON TRUE
Output:
name
Item purchased
Parcel in transit
Charge processed
To see a bit more of what's happening, we can look at:
SELECT *, element_at(name_map, name) as name
id
name
name_map
name
1
buy
{buy=Item purchased, paid=Charge processed, send=Parcel in transit}
Item purchased
2
send
{buy=Item purchased, paid=Charge processed, send=Parcel in transit}
Parcel in transit
3
paid
{buy=Item purchased, paid=Charge processed, send=Parcel in transit}
Charge processed
I'm not sure how efficient this is, but it's certainly an interesting idea.