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
- 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。
end
