plan: use point get plan for UPDATE statement

cmd/explaintest/r/explain_easy.result

@@ -50,8 +50,7 @@ IndexJoin_11	4166.67	root	left outer join, inner:IndexLookUp_10, outer key:test.
   └─TableScan_9	10.00	cop	table:t2, keep order:false, stats:pseudo
 explain update t1 set t1.c2 = 2 where t1.c1 = 1;
 id	count	task	operator info
-TableReader_5	1.00	root	data:TableScan_4
-└─TableScan_4	1.00	cop	table:t1, range:[1,1], keep order:false, stats:pseudo
+Point_Get_1	1.00	root	table:t1, handle:1
 explain delete from t1 where t1.c2 = 1;
 id	count	task	operator info
 IndexLookUp_9	10.00	root	

cmd/explaintest/r/explain_easy_stats.result

@@ -56,8 +56,7 @@ Projection_6	2481.25	root	test.t1.c1, test.t1.c2, test.t1.c3, test.t2.c1, test.t
     └─TableScan_20	1985.00	cop	table:t2, keep order:false
 explain update t1 set t1.c2 = 2 where t1.c1 = 1;
 id	count	task	operator info
-TableReader_5	1.00	root	data:TableScan_4
-└─TableScan_4	1.00	cop	table:t1, range:[1,1], keep order:false
+Point_Get_1	1.00	root	table:t1, handle:1
 explain delete from t1 where t1.c2 = 1;
 id	count	task	operator info
 IndexLookUp_9	0.00	root	

domain/schema_validator_test.go

@@ -95,6 +95,7 @@ func (*testSuite) TestSchemaValidator(c *C) {
 	c.Assert(valid, Equals, ResultUnknown)
 
 	close(exit)
+	time.Sleep(time.Millisecond)
 }
 
 func reload(validator SchemaValidator, leaseGrantCh chan leaseGrantItem, ids ...int64) int64 {

plan/point_get_plan.go

@@ -127,6 +127,8 @@ func tryFastPlan(ctx sessionctx.Context, node ast.Node) Plan {
 			}
 			return fp
 		}
+	case *ast.UpdateStmt:
+		return tryUpdatePointPlan(ctx, x)
 	case *ast.DeleteStmt:
 		return tryDeletePointPlan(ctx, x)
 	}
@@ -382,6 +384,55 @@ func findInPairs(colName string, pairs []nameValuePair) int {
 	return -1
 }
 
+func tryUpdatePointPlan(ctx sessionctx.Context, updateStmt *ast.UpdateStmt) Plan {
+	selStmt := &ast.SelectStmt{
+		Fields:  &ast.FieldList{},
+		From:    updateStmt.TableRefs,
+		Where:   updateStmt.Where,
+		OrderBy: updateStmt.Order,
+		Limit:   updateStmt.Limit,
+	}
+	fastSelect := tryPointGetPlan(ctx, selStmt)
+	if fastSelect == nil {
+		return nil
+	}
+	checkFastPlanPrivilege(ctx, fastSelect, mysql.SelectPriv, mysql.UpdatePriv)
+	orderedList := buildOrderedList(ctx, fastSelect, updateStmt.List)
+	if orderedList == nil {
+		return nil
+	}
+	updatePlan := &Update{
+		SelectPlan:  fastSelect,
+		OrderedList: orderedList,
+	}
+	updatePlan.SetSchema(fastSelect.schema)
+	return updatePlan
+}
+
+func buildOrderedList(ctx sessionctx.Context, fastSelect *PointGetPlan, list []*ast.Assignment) []*expression.Assignment {
+	orderedList := make([]*expression.Assignment, 0, len(list))
+	for _, assign := range list {
+		col, err := fastSelect.schema.FindColumn(assign.Column)
+		if err != nil {
+			return nil
+		}
+		if col == nil {
+			return nil
+		}
+		newAssign := &expression.Assignment{
+			Col: col,
+		}
+		expr, err := expression.RewriteSimpleExprWithSchema(ctx, assign.Expr, fastSelect.schema)
+		if err != nil {
+			return nil
+		}
+		expr = expression.BuildCastFunction(ctx, expr, col.GetType())
+		newAssign.Expr = expr.ResolveIndices(fastSelect.schema)
+		orderedList = append(orderedList, newAssign)
+	}
+	return orderedList
+}
+
 func tryDeletePointPlan(ctx sessionctx.Context, delStmt *ast.DeleteStmt) Plan {
 	if delStmt.IsMultiTable {
 		return nil