Thank you Richard for validating the behaviour against PG. I'm satisfied that this relegate from "possible bug" to "not a bug" under the WWPGD philosophy. I have now also verified that this is the behaviour in MySQL. Here is another variation which I find even less intuitive: ```sql SELECT (SELECT group_concat(a) || '-' || group_concat(b) FROM y) z FROM x; ┌───────┐ │ z │ ├───────┤ │ 1-1,1 │ └───────┘ ``` But again seems consistent (at least with MySQL). --- For context, the goal was to replicate a value as a comma separated list using the out-of-the-box CLI. The failed attempt looked like this: ```sql SELECT (SELECT group_concat(a) FROM generate_series(0,10)) FROM x; ``` And some successful alternatives: ```sql SELECT (SELECT group_concat(a+(value*0)) FROM generate_series(0,10)) FROM x; SELECT group_concat(a) FROM x JOIN generate_series(0,10) GROUP BY x.oid; ```