Multiple tables in CDC expressions

[ale-dd]

For "old style" changefeeds, we have the flexibility to include multiple tables:

{"key":"[822988914618007553]","table":"a","value":"{\"after\": {\"id\": 1, \"rowid\": 822988914618007553}}"}
{"key":"[822988936953397249]","table":"b","value":"{\"after\": {\"id\": 1, \"rowid\": 822988936953397249}}"}

At least when it wouldn't lead to pathological cases, it would be nice to be allowed to reference multiple tables in CDC expressions, as well.

invalid syntax: statement ignored: at or near "join": syntax error
SQLSTATE: 42601
DETAIL: source SQL:
CREATE CHANGEFEED WITH schema_change_policy='stop' AS SELECT *, id as ciao FROM a JOIN b ON a.id = b.id
                                                                                  ^
root@localhost:26257/defaultdb>

Jira issue: CRDB-22541

Epic CRDB-21713

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cc @cockroachdb/cdc

[miretskiy]

Thank you for filing this issue. Joins are not supported with cdc expressions. You can use "old" style changefeeds that allow you to specify multiple tables. But if you want to use "new" style changefeed, you have to restrict your feed to a single table.

Support for streaming joins is non-trivial, and will take a while before (or even if) this feature is supported.

[blathers-crl[bot]]

cc @cockroachdb/cdc

[amruss]

Hey @ale-dd I'm going to leave this on the backlog, but be aware we aren't planning on picking this up anytime soon