建表加约束
建表，其中最后DEAL_FLAG字段不为空，但是值只能在Y和N二选一输入，则可以用check做约束：
USE [test]
CREATE TABLE [dbo].[PUNCH_TBL](SEQ_NBR int NOT NULL,
PUNCH_DAY DATE NOT NULL,
PUNCH_TIME DATE NOT NULL,
PUNCH_TYPE VARCHAR(30) ,
PUNCH_MODE VARCHAR(50) NOT NULL,
BADGE_NBR VARCHAR(50) NOT NULL,
UID VARCHAR(50) ,
MAC_ID VARCHAR(50) NOT NULL,
SERVER_NUM VARCHAR(50),
UPLOAD_TIME DATE NOT NULL,
UPLOAD_TIME2 DATE ,
MAC_TYPE VARCHAR(30) NOT NULL,
LOCATION VARCHAR(255),
DEAL_FLAG VARCHAR(50) NOT NULL,
check (DEAL_FLAG='N' or DEAL_FLAG='Y'))
check约束用法：
http://www.w3school.com.cn/sql/sql_check.asp