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1. BUG #19462: MERGE on partitioned table with INSERT DEFAULT VALUES fails with "unknown action in MERGE WHEN clau

   PG Bug reporting form <noreply@postgresql.org> — 2026-04-20T09:34:09Z

   The following bug has been logged on the website:
   
   Bug reference:      19462
   Logged by:          chunling qin
   Email address:      303677365@qq.com
   PostgreSQL version: 15.0
   Operating system:   centos
   Description:        
   
   ## Summary
   
   A MERGE statement targeting a partitioned table fails with `ERROR: unknown
   action in MERGE WHEN clause` when the NOT MATCHED clause uses `INSERT
   DEFAULT VALUES`.
   
   ## PostgreSQL Version
   
   ```
   PostgreSQL 15devel on x86_64-pc-linux-gnu, compiled by clang version 17.0.6,
   64-bit
   ```
   
   Tested on REL_15_STABLE branch.
   
   ## Steps to Reproduce
   
   ```sql
   -- Setup: Create partitioned target table
   CREATE TABLE pmerge_tgt (id INT) PARTITION BY RANGE (id);
   CREATE TABLE pmerge_tgt_lo PARTITION OF pmerge_tgt FOR VALUES FROM
   (MINVALUE) TO (100);
   CREATE TABLE pmerge_tgt_hi PARTITION OF pmerge_tgt FOR VALUES FROM (100) TO
   (MAXVALUE);
   CREATE TABLE pmerge_tgt_def PARTITION OF pmerge_tgt DEFAULT;
   
   -- Create source table
   CREATE TABLE pmerge_src (id INT);
   
   -- Insert test data
   INSERT INTO pmerge_tgt VALUES (50);
   INSERT INTO pmerge_src VALUES (200);
   
   -- Bug reproduction
   MERGE INTO pmerge_tgt t USING pmerge_src s ON t.id > 1000
     WHEN MATCHED THEN DO NOTHING
     WHEN NOT MATCHED THEN INSERT DEFAULT VALUES;
   ```
   This issue could not be reproduced with the latest version, but we can
   easily reproduced  by  PostgreSQL 15devel. I am submitting this report for
   official confirmation.
   
   -- Bug reproduction
   MERGE INTO pmerge_tgt t USING pmerge_src s ON t.id > 1000
     WHEN MATCHED THEN DO NOTHING
     WHEN NOT MATCHED THEN INSERT DEFAULT VALUES;ERROR:  relation "pmerge_tgt"
   already exists
   postgres=# ERROR:  relation "pmerge_tgt_lo" already exists
   postgres=# ERROR:  relation "pmerge_tgt_hi" already exists
   postgres=# ERROR:  relation "pmerge_tgt_def" already exists
   postgres=# postgres=# postgres=# ERROR:  relation "pmerge_src" already
   exists
   postgres=# postgres=# postgres=# INSERT 0 1
   postgres=# INSERT 0 1
   postgres=# postgres=# postgres=# postgres-# postgres-#
   ERROR:  unknown action in MERGE WHEN clause
   
   
   
   
   
   

2. Re: BUG #19462: MERGE on partitioned table with INSERT DEFAULT VALUES fails with "unknown action in MERGE WHEN clau

   Álvaro Herrera <alvherre@kurilemu.de> — 2026-05-17T20:21:15Z

   On 2026-Apr-20, PG Bug reporting form wrote:
   
   Hello chunling qin,
   
   > ```
   > PostgreSQL 15devel on x86_64-pc-linux-gnu, compiled by clang version 17.0.6,
   > 64-bit
   > ```
   
   > Tested on REL_15_STABLE branch.
   
   Hmm, this is quite an ancient version of 15, right?  I tried your script
   in 15.18 and AFAICT it works correctly.
   
   Thanks,
   
   -- 
   Álvaro Herrera               48°01'N 7°57'E  —  https://www.EnterpriseDB.com/
   "Puedes vivir sólo una vez, pero si lo haces bien, una vez es suficiente"