Oracle single quotation marks problem

Get a single quote:

　　select '''' from dual

　　The end of the beginning and ending at the beginning of a string of single quote character, the second single quote escaping, the third is a single quote

 

select 'test''''' from dual

　　Results for the test ''

　　Is a reference to the beginning and end of a string constant, the remaining analysis from left to right, the first to the second escape