One-off query support

[kazimuth]

Description of Changes

Support one-off queries without establishing a subscription. Took me a while to figure out all the routing. This is (NO LONGER) TOTALLY UNTESTED.

The SQL engine seems to support returning multiple tables so I've routed that through to the client, but I have no idea what queries would actually use that -- @mamcx ?

Also, I don't know how to validate that a query only SELECTs and doesn't do anything else.

@jdetter

[mamcx]

About what queries we support, is all that specified in https://github.com/clockworklabs/SpacetimeDB/tree/master/crates/sqltest when running the validation suite. In concrete https://github.com/clockworklabs/SpacetimeDB/tree/master/crates/sqltest/test/basic are examples of valid queries.

[mamcx]

Also, I don't know how to validate that a query only SELECTs and doesn't do anything else.

Check

SpacetimeDB/crates/core/src/subscription/query.rs

Line 80 in 0f1fdf6

pub fn compile_query(relational_db: &RelationalDB, tx: &MutTxId, input: &str) -> Result<Query, DBError> {

[kazimuth]

@mamcx thanks. Question: I noticed https://github.com/clockworklabs/SpacetimeDB/blob/master/crates/core/src/sql/execute.rs#L86 returns a Vec of Memtables. When will this Vec contain more than one entry?

[mamcx]

When will this Vec contain more than one entry?

For example in

SELECT * FROM table1;SELECT * FROM table2

You can run SQL queries with the cli:

spacetime sql quickstart --interactive

[kazimuth]

This is ready for review @cloutiertyler. Ended up quite short, but I ran into a number of bugs in the process (mainly of my own creation), which ate up a lot of time.

[kulakowski]

And the commit message should probably not say it is ENTIRELY UNTESTED when it lands :)

[kazimuth]

Rebased and squashed, comments addressed. This should be ready for merge

[cloutiertyler]

This seems good to me. I also like the with_read_only fn.

[jdetter]

I was finally able to get this working after some futzing with Unity. I opened this PR to eventually add support for this to our UnitySDK: https://github.com/clockworklabs/com.clockworklabs.spacetimedbsdk/pull/2/files

I've attributed @kazimuth to the commit in the PR. Also @kazimuth would you be willing to write some documentation for this on the website? Maybe it should be part of the API reference. In the future I will work this into the Unity tutorial so that there's better visibility on this.

Thank you James, this is awesome 👍