:= :1

https://docs.oracle.com/cd/A97630_01/appdev.920/a96624/01_oview.htm

https://docs.oracle.com/cd/E11882_01/server.112/e16604/ch_twelve050.htm#SQPUG133

 

Assigning Values to a Variable

 the assignment operator (:=), a colon followed by an equal sign.