在SQLPLUS里面，我们可以使用show all来查看系统的一些设置。
sql> ?show all;
appinfo 为 OFF 并且已设置为 "SQL*Plus"
arraysize 15
autocommit OFF
autoprint OFF
autorecovery OFF
autotrace OFF
blockterminator "." (hex 2e)
btitle OFF 为下一条 SELECT 语句的前几个字符
cmdsep OFF
colsep " "
compatibility version NATIVE
concat "." (hex 2e)
copycommit 0
COPYTYPECHECK 为 ON
define "&" (hex 26)
describe DEPTH 1 LINENUM OFF INDENT ON
echo OFF
editfile "afiedt.buf"
embedded OFF
escape OFF
用于 6 或更多行的 FEEDBACK ON
flagger OFF
flush ON
heading ON
headsep "|" (hex 7c)
instance "local"
linesize 80
lno 14
loboffset 1
logsource ""
long 80
longchunksize 80
markup HTML OFF HEAD "<style type='text/css'> body {font:10pt Arial,Helvetica,sa
ns-serif; color:black; background:White;} p {font:10pt Arial,Helvetica,sans-seri
f; color:black; background:White;} table,tr,td {font:10pt Arial,Helvetica,sans-s
erif; color:Black; background:#f7f7e7; padding:0px 0px 0px 0px; margin:0px 0px 0
px 0px;} th {font:bold 10pt Arial,Helvetica,sans-serif; color:#336699; backgroun
d:#cccc99; padding:0px 0px 0px 0px;} h1 {font:16pt Arial,Helvetica,Geneva,sans-s
erif; color:#336699; background-color:White; border-bottom:1px solid #cccc99; ma
rgin-top:0pt; margin-bottom:0pt; padding:0px 0px 0px 0px;} h2 {font:bold 10pt Ar
ial,Helvetica,Geneva,sans-serif; color:#336699; background-color:White; margin-t
op:4pt; margin-bottom:0pt;} a {font:9pt Arial,Helvetica,sans-serif; color:#66330
0; background:#ffffff; margin-top:0pt; margin-bottom:0pt; vertical-align:top;}</
style><title>SQL*Plus Report</title>" BODY "" TABLE "border='1' width='90%' alig
n='center' summary='Script output'" SPOOL OFF ENTMAP ON PREFORMAT OFF
newpage 1
null ""
numformat ""
numwidth 10
pagesize 14
PAUSE 为 OFF
pno 0
recsep WRAP
recsepchar " " (hex 20)
release 1002000100
repfooter OFF ?为 NULL
repheader OFF ?为 NULL
serveroutput OFF
shiftinout INVISIBLE
showmode OFF
spool OFF
sqlblanklines OFF
sqlcase MIXED
sqlcode 0
sqlcontinue "> "
sqlnumber ON
sqlpluscompatibility 10.2.0
sqlprefix "#" (hex 23)
sqlprompt "SQL> "
sqlterminator ";" (hex 3b)
suffix "sql"
tab ON
termout ON
timing OFF
trimout ON
trimspool OFF
ttitle OFF 为下一条 SELECT 语句的前几个字符
underline "-" (hex 2d)
USER 为 "SYS"
verify ON
wrap : 将换至下一行
这些都是系统的一些设置变量。
实际上，ORACLE还提供了自己定义变量 ?包括define 变量和绑定变量
sql > define x
SQL> define x='abc'
要引用这个变量，需要使用and符号，假如是字符串，需要加上单引号。
SQL> select '&x' from dual;
原值 ? ?1: select '&x' from dual
新值 ? ?1: select 'abc' from dual
'AB
---
abc
================================
绑定变量
要想使用绑定变量，需要先定义它
variable x varchar2(10)
begin
? :x := 'hello';
end;
/
print :x
define 变量总是被sqlplus 扩展的字符串，而declared变量可以被SQL和PLSQL作为真正的绑定变量使用
?