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发布于 2024-12-29 01:13:43 字数 78 浏览 1 评论 0原文

谁能解释一下 SET SCAN OFF 和 SET SCAN ON 的目的是什么？我知道它的目的是禁用替换变量和参数，但我想要一个清晰的解释。

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-残月青衣踏尘吟 2025-01-05 01:13:43

SET SCAN 已过时，但它用于控制是否应扫描替换参数/变量。 OFF 将阻止扫描参数/变量。

SET DEFINE 替换/扩展了功能，这里有一篇很好的文章：http://shaharear.blogspot.com/2009/01/set-define.html

来自网站

设置定义；
从双选择“&hello”；
如果定义设置为 on 并且 SQL*Plus 查找当前替换
前缀，它要求输入一个字符串。在下面的示例中，
我输入：hasan
输入 hello 的值：已输入此字符串

 old 1: select '&hello' from dual 
 new 1: select 'this string was entered' from dual

这相当于旧的 SET SCAN 的工作方式。基本上你正在控制是否提示替换

SET SCAN is obsolete but it was used to control whether or not it should scan for substitution params/variables. OFF would prevent scanning for params/variables.

SET DEFINE replaces/extends the functionality and a good writeup is here: http://shaharear.blogspot.com/2009/01/set-define.html

From the website

set define on;
select '&hello' from dual;
If define is set to on and SQL*Plus finds the current substitution
prefix, it asks for a string to be entered. In the following example,
I entered: hasan
Enter value for hello: this string was entered

 old 1: select '&hello' from dual 
 new 1: select 'this string was entered' from dual

This is equivalent to how the old SET SCAN would work. Basically you're controlling whether or not to prompt for a substitution

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°如果伤别离去 2025-01-05 01:13:43

在 SQL*Plus（以及支持 SQL*Plus 语法的各种其他工具）中，默认情况下，该工具会扫描 SQL 语句以查找替换变量。这允许您创建 SQL*Plus 脚本，使用 SQL*Plus 中定义的变量来执行各种报告任务。

然而，由于替换变量以 & 符号 ('&') 开头，并且不需要提前声明，因此，如果您尝试运行恰好包含 & 符号的 SQL 语句，就会产生问题。例如，如果您的 INSERT 语句恰好包含包含 & 符号的字符串文字，则您不希望 SQL*Plus 预处理该语句。或者，如果我想选择字符串“foo & bar”，

SQL> set scan off;
SQL> ed
Wrote file afiedt.buf

  1* select 'foo & bar' from dual
SQL> /

'FOO&BAR'
---------
foo & bar

但是如果我允许 SQL*Plus 预处理该语句，则文本 '& bar' 被解释为替换变量，系统会提示我输入要在运行时替换的文本

SQL> set scan on
SQL> /
Enter value for bar: some value
old   1: select 'foo & bar' from dual
new   1: select 'foo some value' from dual

'FOOSOMEVALUE'
--------------
foo some value

In SQL*Plus (and various other tools that support SQL*Plus syntax), by default, the tool scans SQL statements looking for substitution variables. This allows you to create SQL*Plus scripts that use variables defined in SQL*Plus for various reporting tasks.

Because substitution variables begin with the ampersand ('&') and need not be declared in advance, however, that creates problems if you are trying to run a SQL statement that happens to include an ampersand. For example, if you've got an INSERT statement that happens to have a string literal that includes an ampersand, you don't want SQL*Plus to pre-process the statement. Or, if I want to select the string "foo & bar"

SQL> set scan off;
SQL> ed
Wrote file afiedt.buf

  1* select 'foo & bar' from dual
SQL> /

'FOO&BAR'
---------
foo & bar

If I allow SQL*Plus to pre-process the statement, however, the text '& bar' is interpreted as a substitution variable and I'm prompted to enter the text to substitute at runtime

SQL> set scan on
SQL> /
Enter value for bar: some value
old   1: select 'foo & bar' from dual
new   1: select 'foo some value' from dual

'FOOSOMEVALUE'
--------------
foo some value

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