From ed4e086df2283ef9a0b02d64ee8083398710924d Mon Sep 17 00:00:00 2001
From: Marius Posta <marius@cockroachlabs.com>
Date: Mon, 4 Oct 2021 16:13:13 -0400
Subject: [PATCH] sql: fix FK check bug in ALTER COLUMN TYPE

This commit fixes an implementation bug when checking that the table's
foreign keys didn't hold a reference to the altered column.

Fixes #71089.

Release note (bug fix): fixes a bug which caused ALTER COLUMN TYPE
statements to fail when they shouldn't have.
---
 pkg/sql/alter_column_type.go                      | 15 ++++++++++++---
 .../testdata/logic_test/alter_column_type         | 10 ++++++++++
 2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/pkg/sql/alter_column_type.go b/pkg/sql/alter_column_type.go
index c3a149a08622..b4ce7e2a5b04 100644
--- a/pkg/sql/alter_column_type.go
+++ b/pkg/sql/alter_column_type.go
@@ -203,9 +203,18 @@ func alterColumnTypeGeneral(
 	// Disallow ALTER COLUMN TYPE general for columns that have a foreign key
 	// constraint.
 	for _, fk := range tableDesc.AllActiveAndInactiveForeignKeys() {
-		for _, id := range append(fk.OriginColumnIDs, fk.ReferencedColumnIDs...) {
-			if col.GetID() == id {
-				return colWithConstraintNotSupportedErr
+		if fk.OriginTableID == tableDesc.GetID() {
+			for _, id := range fk.OriginColumnIDs {
+				if col.GetID() == id {
+					return colWithConstraintNotSupportedErr
+				}
+			}
+		}
+		if fk.ReferencedTableID == tableDesc.GetID() {
+			for _, id := range fk.ReferencedColumnIDs {
+				if col.GetID() == id {
+					return colWithConstraintNotSupportedErr
+				}
 			}
 		}
 	}
diff --git a/pkg/sql/logictest/testdata/logic_test/alter_column_type b/pkg/sql/logictest/testdata/logic_test/alter_column_type
index f3800069fa66..e7beb627f652 100644
--- a/pkg/sql/logictest/testdata/logic_test/alter_column_type
+++ b/pkg/sql/logictest/testdata/logic_test/alter_column_type
@@ -556,3 +556,13 @@ INSERT INTO regression_54844 VALUES (-9223372036854775807)
 
 statement error integer out of range for type int2
 ALTER TABLE regression_54844 ALTER COLUMN i TYPE int2
+
+# Regression test for issue #71089
+subtest regression_71089
+
+statement ok
+CREATE TABLE parent_71089 (id INT PRIMARY KEY);
+CREATE TABLE child_71089 (a INT, b INT REFERENCES parent_71089 (id) NOT NULL)
+
+statement ok
+ALTER TABLE child_71089 ALTER COLUMN a TYPE FLOAT;