extend用法解决方案

extend用法
请问:我想在一可变数组最后加一个元素 "ball ",   用extend应该怎么写啊？
exists怎么用？

[解决办法]
1.Never used extend before. Below method is OK.
select CONCAT(RTRIM( 'aa ', ' ' ' '), 'ball ') from dual
2. Simple sample for exists method.
select ID from tablename
where exists( select id from tablename where id > 10)