有些时候在使用sql*plus时忘记了一些命令的用法，其实我们大可不必到什么地方去查，我们只需要在sql*plus中查看就可以了，
使用help | ？ parameter
例如在sql*plus中：
SQL> help column
COLUMN
------
Specifies display attributes for a given column, such as:
- text for the column heading
- alignment for the column heading
- format for NUMBER data
- wrapping of column data
Also lists the current display attributes for a single column
or all columns.
where option represents one of the following clauses:
ALI[AS] alias
CLE[AR]
ENTMAP {ON|OFF}
FOLD_A[FTER]
FOLD_B[EFORE]
FOR[MAT] format
HEA[DING] text
JUS[TIFY] {L[EFT] | C[ENTER] | R[IGHT]}
LIKE {expr | alias}
NEWL[INE]
NEW_V[ALUE] variable
NOPRI[NT] | PRI[NT]
NUL[L] text
OLD_V[ALUE] variable
ON|OFF
WRA[PPED] | WOR[D_WRAPPED] | TRU[NCATED]
也可以使用？，如下：
SQL> ? show
SHOW
----
Shows the value of a SQL*Plus system variable, or the current
SQL*Plus environment. SHOW SGA requires a DBA privileged login.
where option represents one of the following terms or clauses:
system_variable
ALL
BTI[TLE]
CON_ID
CON_NAME
ERR[ORS] [{FUNCTION | PROCEDURE | PACKAGE | PACKAGE BODY | TRIGGER
| VIEW | TYPE | TYPE BODY | DIMENSION | JAVA CLASS} [schema.]name]
LNO
PARAMETERS [parameter_name]
PDBS
PNO
RECYC[LEBIN] [original_name]
REL[EASE]
REPF[OOTER]
REPH[EADER]
SGA
SPOO[L]
SPPARAMETERS [parameter_name]
SQLCODE
TTI[TLE]
USER
红色的语句就是该命令的sql语句，然后下面就是对它的一些参数的说明。
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