Question

EDIT: Per request here is what’s happening in SQL*Plus
EDIT 2: The issue was the column name being a keyword
SQL> drop table comments;

Table Dropped.

SQL> create table comments (
 2 comment_id number not null,
 3 post_id number not null,
 4 user_id number not null,
 5 message varchar2(2500) not null,
 6 timestamp timestamp(6) not null);

Table Created

SQL> create sequence comment_seq
 2 start with 1
 3 increment by 1
 4 nomaxvalue;

Sequence Created

SQL> ed

Wrote file afiedt.buf //NOTEPAD OPENED UP

1 create or replace trigger comment_trigger
2      before insert on comments
3      for each row
4 begin
5     select comment_seq.nextval
6     into :new.comment_id
7     from dual;
8 end;
SQL> /

    ERROR at Line 2:
    ORA-06552: PL/SQL: Compilation unit analysis terminated
    ORA-06553: PLS-320: the declaration of the type of this expression is
    incomplete or malformed

    SQL> show errors
    No errors.

Answer 1

Assuming I correct the data types of the numeric columns (number(300) is not a valid data type), that code seems to work for me. If you’re getting an error, that implies that you are doing something other than what you’ve posted here.

SQL> create table comments (
  2    comment_id number not null,
  3    post_id    number not null,
  4    user_id    number not null,
  5    message    varchar2(2500) not null,
  6    timestamp  timestamp(6) not null
  7  );

Table created.

SQL> create sequence comment_seq
  2  start with 1
  3  increment by 1
  4  nomaxvalue;

Sequence created.

SQL> ed
Wrote file afiedt.buf

  1  create or replace trigger comment_trigger
  2    before insert on comments
  3    for each row
  4  begin
  5    select comment_seq.nextval
  6      into :new.comment_id
  7      from dual;
  8* end;
SQL> /

Trigger created.