HI, On Jun 28, 2023, 17:26 +0800, Julien Rouhaud <rjuju...@gmail.com>, wrote: > On Wed, Jun 28, 2023 at 05:17:14PM +0800, Julien Rouhaud wrote: > > > > > > Table t1 and t2 both has 2 columns: c1, c2, when CTE join select *, the > > > result target list seems to lost one’s column c1. > > > But it looks good when select cte1.* and t1.* explicitly . > > > > > > Is it a bug? > > > > This is working as intended. When using a USING clause you "merge" both > > columns so the final target list only contain one version of the merged > > columns, which doesn't happen if you use e.g. ON instead. I'm assuming that > > what the SQL standard says, but I don't have a copy to confirm. > > I forgot to mention that this is actually documented: > > https://www.postgresql.org/docs/current/queries-table-expressions.html > > Furthermore, the output of JOIN USING suppresses redundant columns: there is > no > need to print both of the matched columns, since they must have equal values. > While JOIN ON produces all columns from T1 followed by all columns from T2, > JOIN USING produces one output column for each of the listed column pairs (in > the listed order), followed by any remaining columns from T1, followed by any > remaining columns from T2.
Thanks for your help. Regards, Zhang Mingli
