Fix issue #747 (#765)

Co-authored-by: anqiansong <anqiansong@xiaoheiban.cn>

tools/goctl/model/sql/example/sql/user.sql

@@ -3,12 +3,12 @@ CREATE TABLE `user`
 (
     `id`          bigint(10) NOT NULL AUTO_INCREMENT,
     `user`        varchar(50)                             NOT NULL DEFAULT '' COMMENT '用户',
-    `name`        varchar(255) COLLATE utf8mb4_general_ci NOT NULL DEFAULT '' COMMENT '用户\t名称',
+    `name`        varchar(255) COLLATE utf8mb4_general_ci NULL COMMENT '用户\t名称',
     `password`    varchar(255) COLLATE utf8mb4_general_ci NOT NULL DEFAULT '' COMMENT '用户\n密码',
     `mobile`      varchar(255) COLLATE utf8mb4_general_ci NOT NULL DEFAULT '' COMMENT '手机号',
     `gender`      char(5) COLLATE utf8mb4_general_ci      NOT NULL COMMENT '男｜女｜未公\r开',
     `nickname`    varchar(255) COLLATE utf8mb4_general_ci          DEFAULT '' COMMENT '用户昵称',
-    `create_time` timestamp NULL DEFAULT CURRENT_TIMESTAMP,
+    `create_time` timestamp NULL,
     `update_time` timestamp NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
     PRIMARY KEY (`id`),
     UNIQUE KEY `name_index` (`name`),

tools/goctl/model/sql/parser/parser.go

@@ -170,9 +170,7 @@ func convertColumns(columns []*sqlparser.ColumnDefinition, primaryColumn string)
 		if column.Type.NotNull {
 			isDefaultNull = false
 		} else {
-			if column.Type.Default == nil {
-				isDefaultNull = false
-			} else if string(column.Type.Default.Val) != "null" {
+			if column.Type.Default != nil {
 				isDefaultNull = false
 			}
 		}