parser: add 'INSTANT' alter algorithm

ast/ddl.go

@@ -1409,6 +1409,35 @@ const (
 	LockTypeExclusive
 )
 
+// AlterAlgorithm is the algorithm of the DDL operations.
+// See https://dev.mysql.com/doc/refman/8.0/en/alter-table.html#alter-table-performance.
+type AlterAlgorithm byte
+
+// DDL alter algorithms.
+// For now, TiDB only supported inplace and instance algorithms. If the user specify `copy`,
+// will get an error.
+const (
+	AlterAlgorithmDefault AlterAlgorithm = iota
+	AlterAlgorithmCopy
+	AlterAlgorithmInplace
+	AlterAlgorithmInstant
+)
+
+func (a AlterAlgorithm) String() string {
+	switch a {
+	case AlterAlgorithmDefault:
+		return "DEFAULT"
+	case AlterAlgorithmCopy:
+		return "COPY"
+	case AlterAlgorithmInplace:
+		return "INPLACE"
+	case AlterAlgorithmInstant:
+		return "INSTANT"
+	default:
+		return "DEFAULT"
+	}
+}
+
 // AlterTableSpec represents alter table specification.
 type AlterTableSpec struct {
 	node
@@ -1422,6 +1451,7 @@ type AlterTableSpec struct {
 	OldColumnName   *ColumnName
 	Position        *ColumnPosition
 	LockType        LockType
+	Algorithm       AlterAlgorithm
 	Comment         string
 	FromKey         model.CIStr
 	ToKey           model.CIStr
@@ -1543,11 +1573,9 @@ func (n *AlterTableSpec) Restore(ctx *RestoreCtx) error {
 		ctx.WritePlain("= ")
 		ctx.WriteKeyWord(n.LockType.String())
 	case AlterTableAlgorithm:
-		// TODO: not support
 		ctx.WriteKeyWord("ALGORITHM ")
 		ctx.WritePlain("= ")
-		ctx.WriteKeyWord("DEFAULT")
-		ctx.WritePlain(" /* AlterTableAlgorithm is not supported */ ")
+		ctx.WriteKeyWord(n.Algorithm.String())
 	case AlterTableRenameIndex:
 		ctx.WriteKeyWord("RENAME INDEX ")
 		ctx.WriteName(n.FromKey.O)

misc.go

@@ -292,6 +292,7 @@ var tokenMap = map[string]int{
 	"INFILE":                   infile,
 	"INNER":                    inner,
 	"INPLACE":                  inplace,
+	"INSTANT":                  instant,
 	"INSERT":                   insert,
 	"INT":                      intType,
 	"INT1":                     int1Type,