From 645de005a57f021a1b051fb0249505ed503e472d Mon Sep 17 00:00:00 2001
From: zzoraemon043 <195147269+zzoraemon043@users.noreply.github.com>
Date: Mon, 19 Oct 2026 10:19:11 +0800
Subject: [PATCH] Support MERGE in PostgreSQL

Fixes #986
---
 src/languages/postgresql/postgresql.formatter.ts | 6 +++++-
 src/languages/postgresql/postgresql.functions.ts | 3 +++
 test/postgresql.test.ts                          | 2 ++
 3 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/src/languages/postgresql/postgresql.formatter.ts b/src/languages/postgresql/postgresql.formatter.ts
index d3d8a51fd2..912048c283 100644
--- a/src/languages/postgresql/postgresql.formatter.ts
+++ b/src/languages/postgresql/postgresql.formatter.ts
@@ -21,11 +21,15 @@ const reservedClauses = expandPhrases([
   'FOR {UPDATE | NO KEY UPDATE | SHARE | KEY SHARE} [OF]',
   // Data manipulation
   // - insert:
-  'INSERT INTO',
+  'INSERT [INTO]',
   'VALUES',
   'DEFAULT VALUES',
   // - update:
   'SET',
+  // - merge:
+  'MERGE [INTO]',
+  'WHEN [NOT] MATCHED [BY SOURCE | BY TARGET] [THEN]',
+  'UPDATE SET',
   // other
   'RETURNING',
 ]);
diff --git a/src/languages/postgresql/postgresql.functions.ts b/src/languages/postgresql/postgresql.functions.ts
index 6c142e100e..d6e43672be 100644
--- a/src/languages/postgresql/postgresql.functions.ts
+++ b/src/languages/postgresql/postgresql.functions.ts
@@ -271,6 +271,9 @@ export const functions: string[] = [
   'UUID_EXTRACT_TIMESTAMP',
   'UUID_EXTRACT_VERSION',
 
+  // https://www.postgresql.org/docs/17/functions-merge-support.html
+  'MERGE_ACTION',
+
   // https://www.postgresql.org/docs/14/functions-xml.html
   'CURSOR_TO_XML',
   'CURSOR_TO_XMLSCHEMA',
diff --git a/test/postgresql.test.ts b/test/postgresql.test.ts
index e8e99adfea..26fa949af2 100644
--- a/test/postgresql.test.ts
+++ b/test/postgresql.test.ts
@@ -19,6 +19,7 @@ import supportsCreateView from './features/createView.js';
 import supportsIsDistinctFrom from './features/isDistinctFrom.js';
 import supportsArrayLiterals from './features/arrayLiterals.js';
 import supportsDataTypeCase from './options/dataTypeCase.js';
+import supportsMergeInto from './features/mergeInto.js';
 import behavesLikePostgresqlFormatter from './behavesLikePostgresqlFormatter.js';
 
 describe('PostgreSqlFormatter', () => {
@@ -147,6 +148,7 @@ describe('PostgreSqlFormatter', () => {
   supportsParams(format, { numbered: ['$'] });
   supportsLimiting(format, { limit: true, offset: true, fetchFirst: true, fetchNext: true });
   supportsDataTypeCase(format);
+  supportsMergeInto(format);
 
   // Regression test for issue #935
   it('preserves pg_dump restrict commands', () => {