Aside from the SQL syntax, what is the difference between this and the longstanding virtual column feature, where you can define a function that takes the table's record type as input and return a scalar? PostgreSQL already let you use table.funcname as a virtual column, as I recall.
mdaniel•4mo ago
It's possible the following argument is what you meant by "from the SQL syntax," and if so apologies for the noise
At least one demonstrable difference I can see between your recollection and this feature is that the column name being part of the DDL pushes the logic down into the DDL, versus every client having to carry that magic expression around with them. I think it's likely the age-old application-logic-client-side versus stored-proc camps
db=# select id, cast(length(name) AS text)||'0' as silly from my_table
as compared to <<select id, silly from my_table>> for the consumer
saltcured•4mo ago
The virtual column feature I remember is halfway in between. It is not part of the DDL nor reported table schema, so the developer needs to know about it.
But if a function called silly with input type my_table existed, you could still do your second query. It has syntactic sugar for making a bare function name implicitly invoke on the current row record.
I can't remember if that sugar could also be used in an expression index. I never really used this syntactic feature, as I thought being more explicit with function calls would be better coding style.
sharlos201068•4mo ago
That's still not a column and isn't included with things like select *
sgarland•4mo ago
Welp, that’s it. That was the last thing MySQL had that Postgres didn’t (modulo clustering index, which OrioleDB does, soooo…).
Can’t wait!
icedchai•4mo ago
In the past, I've used views to add "virtual columns" where I didn't want to hard code them into the application.
garyclarke27•4mo ago
Stored generated columns would be much more useful if they could reference other rows and tables, they are limited to only the current row.
Automatic incremental view maintenance would also solve this problem, but is unfortunately still a glaring omission in Postgres capabilities.
_el1s7•4mo ago
I don't really find these kind of features necessary.
You can, and probably should, do these things in your application code. I mean, it's not really that hard to make a string lowercase, you don't need to define a "virtual colum" for that...
combatentropy•4mo ago
You're right, it's not that hard. But why would you rather do it there?
saltcured•4mo ago
mdaniel•4mo ago
At least one demonstrable difference I can see between your recollection and this feature is that the column name being part of the DDL pushes the logic down into the DDL, versus every client having to carry that magic expression around with them. I think it's likely the age-old application-logic-client-side versus stored-proc camps
as compared to <<select id, silly from my_table>> for the consumersaltcured•4mo ago
But if a function called silly with input type my_table existed, you could still do your second query. It has syntactic sugar for making a bare function name implicitly invoke on the current row record.
I can't remember if that sugar could also be used in an expression index. I never really used this syntactic feature, as I thought being more explicit with function calls would be better coding style.
sharlos201068•4mo ago