executor: let information_schema be the first database in ShowDatabases

executor/pkg_test.go

@@ -110,3 +110,33 @@ func (s *pkgTestSuite) TestNestedLoopApply(c *C) {
 		}
 	}
 }
+
+func (s *pkgTestSuite) TestMoveInfoSchemaToFront(c *C) {
+	dbss := [][]string{
+		{},
+		{"A", "B", "C", "a", "b", "c"},
+		{"A", "B", "C", "INFORMATION_SCHEMA"},
+		{"A", "B", "INFORMATION_SCHEMA", "a"},
+		{"INFORMATION_SCHEMA"},
+		{"A", "B", "C", "INFORMATION_SCHEMA", "a", "b"},
+	}
+	wanted := [][]string{
+		{},
+		{"A", "B", "C", "a", "b", "c"},
+		{"INFORMATION_SCHEMA", "A", "B", "C"},
+		{"INFORMATION_SCHEMA", "A", "B", "a"},
+		{"INFORMATION_SCHEMA"},
+		{"INFORMATION_SCHEMA", "A", "B", "C", "a", "b"},
+	}
+
+	for _, dbs := range dbss {
+		moveInfoSchemaToFront(dbs)
+	}
+
+	for i, dbs := range wanted {
+		c.Check(len(dbss[i]), Equals, len(dbs))
+		for j, db := range dbs {
+			c.Check(dbss[i][j], Equals, db)
+		}
+	}
+}

executor/show.go

@@ -166,11 +166,25 @@ func (e *ShowExec) fetchShowEngines() error {
 	return nil
 }
 
+// moveInfoSchemaToFront moves information_schema to the first, and the others are sorted in the origin ascending order.
+func moveInfoSchemaToFront(dbs []string) {
+	if len(dbs) > 0 && strings.EqualFold(dbs[0], "INFORMATION_SCHEMA") {
+		return
+	}
+
+	i := sort.SearchStrings(dbs, "INFORMATION_SCHEMA")
+	if i < len(dbs) && strings.EqualFold(dbs[i], "INFORMATION_SCHEMA") {
+		copy(dbs[1:i+1], dbs[0:i])
+		dbs[0] = "INFORMATION_SCHEMA"
+	}
+}
+
 func (e *ShowExec) fetchShowDatabases() error {
 	dbs := e.is.AllSchemaNames()
 	checker := privilege.GetPrivilegeManager(e.ctx)
-	// TODO: let information_schema be the first database
 	sort.Strings(dbs)
+	// let information_schema be the first database
+	moveInfoSchemaToFront(dbs)
 	for _, d := range dbs {
 		if checker != nil && !checker.DBIsVisible(d) {
 			continue

executor/show_test.go

@@ -462,6 +462,30 @@ func (s *testSuite) TestShowVisibility(c *C) {
 	tk.MustExec("drop database showdatabase")
 }
 
+func (s *testSuite) TestShowDatabasesInfoSchemaFirst(c *C) {
+	tk := testkit.NewTestKit(c, s.store)
+	tk.MustQuery("show databases").Check(testkit.Rows("INFORMATION_SCHEMA"))
+	tk.MustExec(`create user 'show'@'%'`)
+	tk.MustExec(`flush privileges`)
+
+	tk.MustExec(`create database AAAA`)
+	tk.MustExec(`create database BBBB`)
+	tk.MustExec(`grant select on AAAA.* to 'show'@'%'`)
+	tk.MustExec(`grant select on BBBB.* to 'show'@'%'`)
+	tk.MustExec(`flush privileges`)
+
+	tk1 := testkit.NewTestKit(c, s.store)
+	se, err := session.CreateSession4Test(s.store)
+	c.Assert(err, IsNil)
+	c.Assert(se.Auth(&auth.UserIdentity{Username: "show", Hostname: "%"}, nil, nil), IsTrue)
+	tk1.Se = se
+	tk1.MustQuery("show databases").Check(testkit.Rows("INFORMATION_SCHEMA", "AAAA", "BBBB"))
+
+	tk.MustExec(`drop user 'show'@'%'`)
+	tk.MustExec(`drop database AAAA`)
+	tk.MustExec(`drop database BBBB`)
+}
+
 // mockSessionManager is a mocked session manager that wraps one session
 // it returns only this session's current process info as processlist for test.
 type mockSessionManager struct {