planner/core: add DefaultExpr support for expressionRewriter

fixes pingcap#4054

planner/core/expression_rewriter.go

@@ -27,6 +27,7 @@ import (
 	"github.com/pingcap/tidb/infoschema"
 	"github.com/pingcap/tidb/sessionctx"
 	"github.com/pingcap/tidb/sessionctx/variable"
+	"github.com/pingcap/tidb/table"
 	"github.com/pingcap/tidb/types"
 	"github.com/pingcap/tidb/types/parser_driver"
 	"github.com/pingcap/tidb/util/chunk"
@@ -169,6 +170,7 @@ type expressionRewriter struct {
 	insertPlan *Insert
 }
 
+// constructBinaryOpFunction converts binary operator functions
 // 1. If op are EQ or NE or NullEQ, constructBinaryOpFunctions converts (a0,a1,a2) op (b0,b1,b2) to (a0 op b0) and (a1 op b1) and (a2 op b2)
 // 2. Else constructBinaryOpFunctions converts (a0,a1,a2) op (b0,b1,b2) to
 // `IF( a0 NE b0, a0 op b0,
@@ -798,6 +800,8 @@ func (er *expressionRewriter) Leave(originInNode ast.Node) (retNode ast.Node, ok
 		er.isNullToExpression(v)
 	case *ast.IsTruthExpr:
 		er.isTrueToScalarFunc(v)
+	case *ast.DefaultExpr:
+		er.evalDefaultExpr(v)
 	default:
 		er.err = errors.Errorf("UnknownType: %T", v)
 		return retNode, false
@@ -1276,3 +1280,47 @@ func (er *expressionRewriter) toColumn(v *ast.ColumnName) {
 	}
 	er.err = ErrUnknownColumn.GenWithStackByArgs(v.String(), clauseMsg[er.b.curClause])
 }
+
+func (er *expressionRewriter) evalDefaultExpr(v *ast.DefaultExpr) {
+	col, err := er.schema.FindColumn(v.Name)
+	if err != nil {
+		er.err = errors.Trace(err)
+		return
+	}
+
+	table, err := er.b.is.TableByName(col.DBName, col.OrigTblName)
+	if err != nil {
+		er.err = errors.Trace(err)
+		return
+	}
+
+	var val *expression.Constant
+	for _, col := range table.Cols() {
+		if col.Name.L == v.Name.Name.L {
+			// if column default value is 'current_timestamp', use NULL to be compatible with MySQL 5.7
+			if hasCurrentTimestampDefault(col) {
+				val = expression.Null
+			} else {
+				val, er.err = er.b.getDefaultValue(col)
+			}
+			break
+		}
+	}
+	if er.err != nil {
+		return
+	}
+	stkLen := len(er.ctxStack)
+	er.ctxStack = er.ctxStack[:stkLen-1]
+	er.ctxStack = append(er.ctxStack, val)
+}
+
+func hasCurrentTimestampDefault(col *table.Column) bool {
+	if col.Tp != mysql.TypeTimestamp && col.Tp != mysql.TypeDatetime {
+		return false
+	}
+	x, ok := col.DefaultValue.(string)
+	if !ok {
+		return false
+	}
+	return strings.ToUpper(x) == strings.ToUpper(ast.CurrentTimestamp)
+}

planner/core/expression_rewriter_test.go

@@ -17,6 +17,7 @@ import (
 	. "github.com/pingcap/check"
 	"github.com/pingcap/tidb/util/testkit"
 	"github.com/pingcap/tidb/util/testleak"
+	"github.com/pingcap/tidb/util/testutil"
 )
 
 var _ = Suite(&testExpressionRewriterSuite{})
@@ -58,3 +59,46 @@ func (s *testExpressionRewriterSuite) TestBinaryOpFunction(c *C) {
 	tk.MustQuery("SELECT * FROM t WHERE (a,b,c) <= (1,2,3) order by b").Check(testkit.Rows("1 1 <nil>", "1 2 3"))
 	tk.MustQuery("SELECT * FROM t WHERE (a,b,c) > (1,2,3) order by b").Check(testkit.Rows("1 3 <nil>"))
 }
+
+func (s *testExpressionRewriterSuite) TestDefaultFunction(c *C) {
+	defer testleak.AfterTest(c)()
+	store, dom, err := newStoreWithBootstrap()
+	c.Assert(err, IsNil)
+	tk := testkit.NewTestKit(c, store)
+	defer func() {
+		dom.Close()
+		store.Close()
+	}()
+	tk.MustExec("use test")
+	tk.MustExec("drop table if exists t1")
+	tk.MustExec(`create table t1(
+		a varchar(10) default 'def',
+		b varchar(10),
+		c int default '10',
+		d double default '3.14',
+		e datetime default '20180101',
+		f datetime default current_timestamp);`)
+	tk.MustExec("insert into t1(a, b, c, d) values ('1', '1', 1, 1)")
+	tk.MustQuery(`select
+		default(a) as defa, 
+		default(b) as defb,
+		default(c) as defc,
+		default(d) as defd,
+		default(e) as defe,
+		default(f) as deff
+		from t1`).Check(testutil.RowsWithSep("|", "def|<nil>|10|3.14|2018-01-01 00:00:00|<nil>"))
+
+	tk.MustExec("create table t2(a varchar(10), b varchar(10))")
+	tk.MustExec("insert into t2 values ('1', '1')")
+	_, err = tk.Exec("select default(a) from t1, t2")
+	c.Assert(err, NotNil)
+	tk.MustQuery("select default(t1.a) from t1, t2").Check(testkit.Rows("def"))
+
+	tk.MustExec("prepare stmt from 'select default(a) from t1';")
+	tk.MustQuery("execute stmt").Check(testkit.Rows("def"))
+	tk.MustExec("alter table t1 modify a varchar(10) default 'DEF'")
+	tk.MustQuery("execute stmt").Check(testkit.Rows("DEF"))
+
+	tk.MustExec("update t1 set c = c + default(c)")
+	tk.MustQuery("select c from t1").Check(testkit.Rows("11"))
+}