[转帖]关于Java中SQL语句的拼接规则

Posted 2022-06-09 jinanxiaolaohu

 

自学demo 的时候遇到的问题 

结果应该是

‘"+e.getName()+"‘

注意 一共有三组标点符号 (除去 方法函数后面的括号)

 

实现目标语句是这个
注意，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，如果字符串中需要拼接变量，该变量用单引号括起来，然后加两个双引号再加两个加号，中间就是变量。

拼接步骤

1. 写出SQL具体语句（无变量都是具体值的），比如上面的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改为id（int类型变量），只需要在中间修改
   ，先是删掉2，用单引‘ ‘代替

   String sql = "SELECT id, piUrl FROM picinfos WHERE id BETWEEN  ‘  ‘ AND 10" ;

   3.接着在单引号中间加上双引" "

   String sql = "SELECT id, piUrl FROM picinfos WHERE id BETWEEN  ‘ "    " ‘ AND 10" ;

   4.接着在双引号中间加上加号+ +

   String sql = "SELECT id, piUrl FROM picinfos WHERE id BETWEEN  ‘ " +  + " ‘ AND 10" ;

   5.最后就是加号中间加上变量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，中间加双引，中间加双加号，中间加变量。