My Favorite PostgreSQL 18 Feature: Virtual Generated Columns

My Favorite PostgreSQL 18 Feature: Virtual Generated Columns(tselai.com)

54 points by fforflo 249 days ago | 9 comments

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.

saltcured 248 days ago |

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 248 days 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 248 days 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 248 days ago | |

That's still not a column and isn't included with things like select *

icedchai 248 days ago |

In the past, I've used views to add "virtual columns" where I didn't want to hard code them into the application.

sgarland 248 days 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!

_el1s7 248 days 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 247 days ago | |

You're right, it's not that hard. But why would you rather do it there?