你知道你类似下面的操作时,内存中生成了多少个新的字符串吗?
sqlSelect = "select StoreCode,TerminalID,SequenceNo from HTPOrderTransaction"
+ " where StoreCode = " + storeCode
+ " and TerminalID = '" + terminalID
+ "' and SequenceNo = " + sequenceNo;
建议直接使用@符号,然后直接敲回车
至于你非要拼接字符串的地方可以使用如下方法
string sqlSelect = string.Format("select StoreCode,TerminalID,SequenceNo from HTPOrderTransaction where StoreCode = {0} and TerminalID = '{1}' and SequenceNo = {2}",storeCode,terminalID,sequenceNo);
如storeCode=11,terminalID="11",sequenceNo=11
则等同与 sqlSelect = select StoreCode,TerminalID,SequenceNo from HTPOrderTransaction where StoreCode = 11 and TerminalID = '11' and SequenceNo=11;
加号是用来连接的,sqlSelect是一个字符串,所以内容要用双引号.在数据库中查询字符串要用单引号的.
sqlSelect = "select StoreCode,TerminalID,SequenceNo from HTPOrderTransaction"
+ " where StoreCode = " + storeCode
+ " and TerminalID = '" + terminalID
+ "' and SequenceNo = " + sequenceNo;
的实际操作意思就是sqlSelect=select StoreCode,TerminalID,SequenceNo from HTPOrderTransaction
where StoreCode =storeCode and TerminalID ='terminalID' and SequenceNo =sequenceNo;
每一对双引号表示一个字符串常量,双引号中间的是字符串内容
加号是用于字符串连接