Why do C-style comments make insert statement run twice?

Question

To make a long story short, I started getting ORA-00001 primary key violations and I tracked down the issue to the fact that some of my INSERT INTO statements were

Answer 1

/* This is a comment */

Just make sure you have a space after /* ,
So it is treated as a single/multi line comment. And not mean to execute the last stored PL/SQL or SQL

To put it in detail.

What ever SQL*Plus interprets after / is ignored and it blindly pushes it's cached block into the server. Except for /* followed by a new line or space.

SQL> SELECT * FROM DUAL;

D
-
X

SQL> /*t*/

D
-
X

SQL> /*
SQL> */
SQL> /

D
-
X

SQL> /*s

D
-
X

From Document:

You must enter a space after the slash-asterisk(/*) beginning a comment.