From aee4fd26f0c4927fd9e7f32208441f22ad481dd7 Mon Sep 17 00:00:00 2001
From: Mattias Jonsson <mattias.jonsson@pingcap.com>
Date: Mon, 22 Nov 2021 01:21:43 +0100
Subject: [PATCH] fix for INSERT INTO t SET timestamp_col = DEFAULT (#29926)

---
 parser/ast/expressions.go           |  5 ++++-
 parser/parser.y                     |  4 +---
 planner/core/expression_rewriter.go | 16 ++++++++++++++--
 planner/core/planbuilder.go         |  3 ++-
 4 files changed, 21 insertions(+), 7 deletions(-)

diff --git a/parser/ast/expressions.go b/parser/ast/expressions.go
index 6a46ab332c831..412e75edd0af9 100644
--- a/parser/ast/expressions.go
+++ b/parser/ast/expressions.go
@@ -606,12 +606,15 @@ type DefaultExpr struct {
 	exprNode
 	// Name is the column name.
 	Name *ColumnName
+	// True - DEFAULT(ColumnName), False - just DEFAULT, but name filled in afterwards
+	// like for: INSERT INTO t1 SET t = DEFAULT
+	NameIsGiven bool
 }
 
 // Restore implements Node interface.
 func (n *DefaultExpr) Restore(ctx *format.RestoreCtx) error {
 	ctx.WriteKeyWord("DEFAULT")
-	if n.Name != nil {
+	if n.NameIsGiven && n.Name != nil {
 		ctx.WritePlain("(")
 		if err := n.Name.Restore(ctx); err != nil {
 			return errors.Annotate(err, "An error occurred while restore DefaultExpr.Name")
diff --git a/parser/parser.y b/parser/parser.y
index e339af5ed92da..deade84a1d860 100644
--- a/parser/parser.y
+++ b/parser/parser.y
@@ -6207,7 +6207,6 @@ ProcedureCall:
  *
  *  Insert Statements
  *
- *  TODO: support PARTITION
  **********************************************************************************/
 InsertIntoStmt:
 	"INSERT" TableOptimizerHintsOpt PriorityOpt IgnoreOptional IntoOpt TableName PartitionNameListOpt InsertValues OnDuplicateKeyUpdate
@@ -6381,7 +6380,6 @@ OnDuplicateKeyUpdate:
  *  Replace Statements
  *  See https://dev.mysql.com/doc/refman/5.7/en/replace.html
  *
- *  TODO: support PARTITION
  **********************************************************************************/
 ReplaceIntoStmt:
 	"REPLACE" PriorityOpt IntoOpt TableName PartitionNameListOpt InsertValues
@@ -6848,7 +6846,7 @@ SimpleExpr:
 	}
 |	"DEFAULT" '(' SimpleIdent ')'
 	{
-		$$ = &ast.DefaultExpr{Name: $3.(*ast.ColumnNameExpr).Name}
+		$$ = &ast.DefaultExpr{Name: $3.(*ast.ColumnNameExpr).Name NameIsGiven: true}
 	}
 |	"VALUES" '(' SimpleIdent ')' %prec lowerThanInsertValues
 	{
diff --git a/planner/core/expression_rewriter.go b/planner/core/expression_rewriter.go
index 570c5b30c8b56..38f6bb5cf56ab 100644
--- a/planner/core/expression_rewriter.go
+++ b/planner/core/expression_rewriter.go
@@ -1941,11 +1941,23 @@ func (er *expressionRewriter) evalDefaultExpr(v *ast.DefaultExpr) {
 	isCurrentTimestamp := hasCurrentDatetimeDefault(col)
 	var val *expression.Constant
 	switch {
-	case isCurrentTimestamp && col.Tp == mysql.TypeDatetime:
+	case isCurrentTimestamp && !v.NameIsGiven && (col.Tp == mysql.TypeDatetime || col.Tp == mysql.TypeTimestamp):
+		// SET col = DEFAULT
+		t, err := expression.GetTimeValue(er.sctx, ast.CurrentTimestamp, col.Tp, int8(col.Decimal))
+		if err != nil {
+			return
+		}
+		val = &expression.Constant{
+			Value:   t,
+			RetType: types.NewFieldType(col.Tp),
+		}
+	case isCurrentTimestamp && v.NameIsGiven && col.Tp == mysql.TypeDatetime:
 		// for DATETIME column with current_timestamp, use NULL to be compatible with MySQL 5.7
+		// DEFAULT(colname)
 		val = expression.NewNull()
-	case isCurrentTimestamp && col.Tp == mysql.TypeTimestamp:
+	case isCurrentTimestamp && v.NameIsGiven && col.Tp == mysql.TypeTimestamp:
 		// for TIMESTAMP column with current_timestamp, use 0 to be compatible with MySQL 5.7
+		// DEFAULT(colname)
 		zero := types.NewTime(types.ZeroCoreTime, mysql.TypeTimestamp, int8(col.Decimal))
 		val = &expression.Constant{
 			Value:   types.NewDatum(zero),
diff --git a/planner/core/planbuilder.go b/planner/core/planbuilder.go
index d1fc3ba01cdc3..105a0427bab2e 100644
--- a/planner/core/planbuilder.go
+++ b/planner/core/planbuilder.go
@@ -3215,7 +3215,8 @@ func (b *PlanBuilder) buildSetValuesOfInsert(ctx context.Context, insert *ast.In
 	insertPlan.AllAssignmentsAreConstant = true
 	for i, assign := range insert.Setlist {
 		defaultExpr := extractDefaultExpr(assign.Expr)
-		if defaultExpr != nil {
+		if defaultExpr != nil && !defaultExpr.NameIsGiven {
+			// Set the name of the column in the assignment
 			defaultExpr.Name = assign.Column
 		}
 		// Note: For INSERT, REPLACE, and UPDATE, if a generated column is inserted into, replaced, or updated explicitly, the only permitted value is DEFAULT.