java sql语句如何写
关于Java中SQL语句的拼接划定规矩
实现目标语句是下面这个,注重,这里的java变量是idd
int idd; String sql = "SELECT id, piUrl FROM picinfos WHERE id BETWEEN '" + idd + "' AND 10" ;
java中的字符串只能双引号,假如字符串中须要拼接变量,该变量用单引号括起来,然后加两个双引号再加两个加号,中心就是变量。
拼接步骤
1.写出SQL细致语句(无变量都是细致值的),比方上面的sql
//查询picinfos表中id为2到10的id和piUrl值 String sql = "SELECT id, piUrl FROM picinfos WHERE id BETWEEN 2 AND 10" ;
2.此时要将2改成id(int范例变量),只须要在中心修正,先是删掉2,用单引' '替代
String sql = "SELECT id, piUrl FROM picinfos WHERE id BETWEEN ' ' AND 10" ;
3.接着在单引号中心加上双引" "
String sql = "SELECT id, piUrl FROM picinfos WHERE id BETWEEN ' " " ' AND 10" ;
4.接着在双引号中心加上加号+ +
String sql = "SELECT id, piUrl FROM picinfos WHERE id BETWEEN ' " + + " ' AND 10" ;
5.末了就是加号中心加上变量idd完事
String sql = "SELECT id, piUrl FROM picinfos WHERE id BETWEEN ' " + idd + " ' AND 10" ;
口诀:先SQL原型,替换为单引,中心加双引,中心加双加号,中心加变量。
那末java的字符串究竟是如何转化为SQL语句的呢
如图所示
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