From 4e713e69a8f52c8235be4ae5ea361997d99887e0 Mon Sep 17 00:00:00 2001
From: emirmrkaljevic <93012621+emirmrkaljevic@users.noreply.github.com>
Date: Wed, 14 Oct 2026 10:53:38 +0200
Subject: [PATCH] Support MERGE statement in PostgreSQL

Closes #986
---
 .../postgresql/postgresql.formatter.ts        |  6 +++-
 .../postgresql/postgresql.functions.ts        |  3 ++
 test/postgresql.test.ts                       | 28 +++++++++++++++++++
 3 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/src/languages/postgresql/postgresql.formatter.ts b/src/languages/postgresql/postgresql.formatter.ts
index d3d8a51fd2..324d2a79c6 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..c18a2520c4 100644
--- a/src/languages/postgresql/postgresql.functions.ts
+++ b/src/languages/postgresql/postgresql.functions.ts
@@ -710,6 +710,9 @@ export const functions: string[] = [
   // https://www.postgresql.org/docs/14/functions-statistics.html
   'PG_MCV_LIST_ITEMS',
 
+  // https://www.postgresql.org/docs/17/functions-merge-support.html
+  'MERGE_ACTION',
+
   // cast
   'CAST',
 ];
diff --git a/test/postgresql.test.ts b/test/postgresql.test.ts
index e8e99adfea..8e6570b799 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 +148,33 @@ describe('PostgreSqlFormatter', () => {
   supportsParams(format, { numbered: ['$'] });
   supportsLimiting(format, { limit: true, offset: true, fetchFirst: true, fetchNext: true });
   supportsDataTypeCase(format);
+  supportsMergeInto(format);
+
+  // Issue #986
+  it('formats MERGE with PostgreSQL 17 additions', () => {
+    const result = format(
+      `MERGE INTO stock t USING incoming s ON t.sku = s.sku
+      WHEN MATCHED AND s.qty = 0 THEN DELETE
+      WHEN NOT MATCHED BY SOURCE THEN DO NOTHING
+      WHEN NOT MATCHED BY TARGET THEN INSERT VALUES (s.sku, s.qty)
+      RETURNING merge_action(), t.*;`
+    );
+    expect(result).toBe(dedent`
+      MERGE INTO
+        stock t USING incoming s ON t.sku = s.sku
+      WHEN MATCHED
+        AND s.qty = 0 THEN DELETE
+      WHEN NOT MATCHED BY SOURCE THEN
+        DO NOTHING
+      WHEN NOT MATCHED BY TARGET THEN
+      INSERT
+      VALUES
+        (s.sku, s.qty)
+      RETURNING
+        merge_action(),
+        t.*;
+    `);
+  });
 
   // Regression test for issue #935
   it('preserves pg_dump restrict commands', () => {