What is the significance of a semicolon at the end of SQL*Plus commands?

Question

Some statements like create table, insert into etc take a semicolon at the end:

CREATE TABLE employees_demo
    ( employee_id    NUMBER(6)
    , first_name     VARCHAR2(20)
    , last_name      VARCHAR2(25) 
         CONSTRAINT emp_last_name_nn_demo NOT NULL
    ) ;

while others like

set echo on
connect system/manager

go through without the semicolon as well.

What is the reasoning behind this? How can I decide myself where to put the semicolon and where not?

Answer 1

Commants to the local instance execute on return. Multi-line commands to the server execute on semicolon

Special commands as detailed in the SQL*Plus manual are the only ones that do not accept semi-colons. Wheras SQL Commands must end with a ; in order to be parsed by the server.

Answer 2

When you're entering an SQL statement into SQL*Plus, it needs to know when you're done with it, especially if the command spans multple rows. Therefore, it requires a terminal character character which can be set with the set sqlterminator. By default, this character is the semicolon:

SQL> select *
  2  from
  3  dual;

D
-
X

Now, changing this terminal character to a #:

SQL> set sqlterminator #
SQL> select *
  2  from
  3  dual#

D
-
X

The SQL statement was ended (end executed) with a #.

You ask: why was set sqlterminator # not followed by a semicolon? Answer, because this is not an SQL statement. Statements that relate to SQL*Plus and its behaviour, output, connection asf (such as set echo on and connect system/manager) are not SQL statements and are therfore entered without the semicolon.

What has this to do with the /?

When you entered an SQL statement, SQL*plus filled something what it calls a buffer. This buffer can be shown with the list command:

SQL> list
  1  select *
  2  from
  3* dual
SQL>

(Note: I only entered list, the rest is returned)

The / now executes what is currently in the buffer. Lets try that:

SQL> /

D
-
X

As can be seen, the same query is executed.

Answer 3

The semicolon is the sequence point for the SQL parser, whereas commands that are executed within SQL*Plus are executed immediately anyway. As an analogy, compare the semicolons in a C program to the commands entered into the shell.

Answer 4

The way I understand it is that the general SQL parser shares a lot in common with the general javascript parser, in that it would like a semicolon after every appropriate place, but it's not required except in certain circumstances. When I was taught to write SQL, I was told a semicolon was part of the language, not an extra operator we could ignore.