ddl: set proper default flen of decimal(0) columns (#54028) (#54619)

close #53779

pkg/planner/core/preprocess.go

@@ -1415,21 +1415,22 @@ func checkColumn(colDef *ast.ColumnDef) error {
 			}
 		}
 	case mysql.TypeNewDecimal:
-		if tp.GetDecimal() > mysql.MaxDecimalScale {
-			return types.ErrTooBigScale.GenWithStackByArgs(tp.GetDecimal(), colDef.Name.Name.O, mysql.MaxDecimalScale)
+		tpFlen := tp.GetFlen()
+		tpDecimal := tp.GetDecimal()
+		if tpDecimal > mysql.MaxDecimalScale {
+			return types.ErrTooBigScale.GenWithStackByArgs(tpDecimal, colDef.Name.Name.O, mysql.MaxDecimalScale)
 		}
-
-		if tp.GetFlen() > mysql.MaxDecimalWidth {
-			return types.ErrTooBigPrecision.GenWithStackByArgs(tp.GetFlen(), colDef.Name.Name.O, mysql.MaxDecimalWidth)
+		if tpFlen > mysql.MaxDecimalWidth {
+			return types.ErrTooBigPrecision.GenWithStackByArgs(tpFlen, colDef.Name.Name.O, mysql.MaxDecimalWidth)
 		}
-
-		if tp.GetFlen() < tp.GetDecimal() {
+		if tpFlen < tpDecimal {
 			return types.ErrMBiggerThanD.GenWithStackByArgs(colDef.Name.Name.O)
 		}
 		// If decimal and flen all equals 0, just set flen to default value.
-		if tp.GetDecimal() == 0 && tp.GetFlen() == 0 {
+		if tpFlen == 0 && (tpDecimal == 0 || tpDecimal == types.UnspecifiedLength) {
 			defaultFlen, _ := mysql.GetDefaultFieldLengthAndDecimal(mysql.TypeNewDecimal)
 			tp.SetFlen(defaultFlen)
+			tp.SetDecimal(0)
 		}
 	case mysql.TypeBit:
 		if tp.GetFlen() <= 0 {

tests/integrationtest/r/ddl/column.result

@@ -57,3 +57,11 @@ t2	CREATE TABLE `t2` (
   PRIMARY KEY (`id`) /*T![clustered_index] CLUSTERED */,
   UNIQUE KEY `authorIdx` (`authorId`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin
+drop table if exists t;
+create table t(a decimal(0,0), b decimal(0));
+show create table t;
+Table	Create Table
+t	CREATE TABLE `t` (
+  `a` decimal(10,0) DEFAULT NULL,
+  `b` decimal(10,0) DEFAULT NULL
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin

tests/integrationtest/t/ddl/column.test

@@ -18,3 +18,7 @@ show create table t1;
 CREATE TABLE `t2`( `id` INTEGER PRIMARY KEY, `authorId` int(11) AUTO_INCREMENT, UNIQUE KEY `authorIdx` (`authorId`));
 show create table t2;
 
+# TestIssue53779
+drop table if exists t;
+create table t(a decimal(0,0), b decimal(0));
+show create table t;