set_scan.txt

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DEF[INE] {&|c|OFF|ON} 
Sets the character used to prefix substitution variables to c. 
ON or OFF controls whether SQL*Plus will scan commands for substitution variables 
and replace them with their values. 
ON changes the value of c back to the default '&', not the most recently used character.
 The setting of DEFINE to OFF overrides the setting of the SCAN variable.
 For more information on the SCAN variable, see the SET SCAN command in Appendix F. 

Controls scanning for the presence of substitution variables and parameters. OFF 
suppresses processing of substitution variables and parameters; ON allows normal processing. 

Syntax
SET SCAN {OFF|ON}

Usage Notes
ON functions in the same manner as SET DEFINE ON. 

set scan off :禁止对置换变量的扫描。把&var就当作一个普通字符。
set scan off
--此句sql存为select.sql
--select * from $table;

@c:/select.sql
set scan on
@c:/select.sql