Not everybody knows that in SQL Plus the character # (called hash or pound) has a special use that I discovered it myself not much time ago. Well, it’s not really a secret, you can read about it on the official SQL Plus manual, but it’s rarely used. The sign #, in fact, is the default character used as SQLPREFIX during a SQL Plus session and can be changed executing the command
SET SQLPRE[FIX] prefix_char
But what does it do? It tells SQL Plus to execute a SQL Plus command while in the middle of entering a SQL statement or a Pl/Sql block of code.
For example you are writing a select statement
SQL> select empno, ename,
and, while writing down the list of columns to extract, you don’t remember the name of one of them. Normally you would quit writing the query, execute a desc of the table and start writing it again from scratch. But the # sign give us another possibility. All you have to do is enter a new line, digit the magic sign # and write the desc you need