From 64085d8a348161fbb09f7ad65f5c00a346a35eac Mon Sep 17 00:00:00 2001
From: Shlomi Noach <2607934+shlomi-noach@users.noreply.github.com>
Date: Wed, 25 Oct 2023 11:52:08 +0300
Subject: [PATCH] Online DDL: support DROP FOREIGN KEY statement (#14338)

Signed-off-by: Shlomi Noach <2607934+shlomi-noach@users.noreply.github.com>
---
 .../onlineddl/scheduler/onlineddl_scheduler_test.go   |  6 ++++++
 go/vt/vttablet/onlineddl/executor.go                  |  4 ++--
 go/vt/vttablet/onlineddl/executor_test.go             | 11 +++++++++++
 3 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/go/test/endtoend/onlineddl/scheduler/onlineddl_scheduler_test.go b/go/test/endtoend/onlineddl/scheduler/onlineddl_scheduler_test.go
index 057c937d6cf..031751bc775 100644
--- a/go/test/endtoend/onlineddl/scheduler/onlineddl_scheduler_test.go
+++ b/go/test/endtoend/onlineddl/scheduler/onlineddl_scheduler_test.go
@@ -2122,6 +2122,12 @@ func testForeignKeys(t *testing.T) {
 			allowForeignKeys: true,
 			expectHint:       "new_fk",
 		},
+		{
+			name:             "drop foreign key from a child",
+			sql:              "alter table child_table DROP FOREIGN KEY child_parent_fk",
+			allowForeignKeys: true,
+			expectHint:       "child_hint",
+		},
 	}
 
 	createParams := func(ddlStatement string, ddlStrategy string, executeStrategy string, expectHint string, expectError string, skipWait bool) *testOnlineDDLStatementParams {
diff --git a/go/vt/vttablet/onlineddl/executor.go b/go/vt/vttablet/onlineddl/executor.go
index 746edbd6948..e296bf026d8 100644
--- a/go/vt/vttablet/onlineddl/executor.go
+++ b/go/vt/vttablet/onlineddl/executor.go
@@ -1195,8 +1195,8 @@ func (e *Executor) validateAndEditAlterTableStatement(ctx context.Context, onlin
 	validateWalk := func(node sqlparser.SQLNode) (kontinue bool, err error) {
 		switch node := node.(type) {
 		case *sqlparser.DropKey:
-			if node.Type == sqlparser.CheckKeyType {
-				// drop a check constraint
+			if node.Type == sqlparser.CheckKeyType || node.Type == sqlparser.ForeignKeyType {
+				// drop a check or a foreign key constraint
 				mappedName, ok := constraintMap[node.Name.String()]
 				if !ok {
 					return false, vterrors.Errorf(vtrpcpb.Code_INTERNAL, "Found DROP CONSTRAINT: %v, but could not find constraint name in map", sqlparser.CanonicalString(node))
diff --git a/go/vt/vttablet/onlineddl/executor_test.go b/go/vt/vttablet/onlineddl/executor_test.go
index b642921d831..691891c4af7 100644
--- a/go/vt/vttablet/onlineddl/executor_test.go
+++ b/go/vt/vttablet/onlineddl/executor_test.go
@@ -158,6 +158,7 @@ func TestValidateAndEditAlterTableStatement(t *testing.T) {
 	e := Executor{}
 	tt := []struct {
 		alter  string
+		m      map[string]string
 		expect []string
 	}{
 		{
@@ -208,6 +209,13 @@ func TestValidateAndEditAlterTableStatement(t *testing.T) {
 			alter:  "alter table t add constraint t_fk_1 foreign key (parent_id) references onlineddl_test_parent (id) on delete no action, add constraint some_check check (id != 1)",
 			expect: []string{"alter table t add constraint fk_1_6fmhzdlya89128u5j3xapq34i foreign key (parent_id) references onlineddl_test_parent (id) on delete no action, add constraint some_check_aulpn7bjeortljhguy86phdn9 check (id != 1), algorithm = copy"},
 		},
+		{
+			alter: "alter table t drop foreign key t_fk_1",
+			m: map[string]string{
+				"t_fk_1": "fk_1_aaaaaaaaaaaaaa",
+			},
+			expect: []string{"alter table t drop foreign key fk_1_aaaaaaaaaaaaaa, algorithm = copy"},
+		},
 	}
 	for _, tc := range tt {
 		t.Run(tc.alter, func(t *testing.T) {
@@ -217,6 +225,9 @@ func TestValidateAndEditAlterTableStatement(t *testing.T) {
 			require.True(t, ok)
 
 			m := map[string]string{}
+			for k, v := range tc.m {
+				m[k] = v
+			}
 			onlineDDL := &schema.OnlineDDL{UUID: "a5a563da_dc1a_11ec_a416_0a43f95f28a3", Table: "t", Options: "--unsafe-allow-foreign-keys"}
 			alters, err := e.validateAndEditAlterTableStatement(context.Background(), onlineDDL, alterTable, m)
 			assert.NoError(t, err)