Oracle PL / SQL代码中的神秘声明(Mysterious declaration in Oracle PL/SQL code)

Oracle PL / SQL代码中的神秘声明(Mysterious declaration in Oracle PL/SQL code)

什么是Oracle PL / SQL中的这个&n声明？ 代码示例（取自此处 ）的用法如下所示：

DECLARE myex EXCEPTION; PRAGMA EXCEPTION_INIT(myex,-20015); n NUMBER := &n; BEGIN FOR i IN 1..n LOOP dbms_output.put.line(i); IF i=n THEN RAISE myex; END IF; END LOOP; EXCEPTION WHEN myex THEN dbms_output.put.line('loop is end'); END;

What means this &n declaration in Oracle PL/SQL? Usage in code sample (taken from here) is shown below:

DECLARE myex EXCEPTION; PRAGMA EXCEPTION_INIT(myex,-20015); n NUMBER := &n; BEGIN FOR i IN 1..n LOOP dbms_output.put.line(i); IF i=n THEN RAISE myex; END IF; END LOOP; EXCEPTION WHEN myex THEN dbms_output.put.line('loop is end'); END;

最满意答案

&n是一个替代变量 。

在语句中使用替换变量时，SQL * Plus会请求一个输入值并重写该语句以包含它。 重写的语句被传递给数据库。 因此，数据库服务器对替换变量一无所知。

&n is a substitution variable.

When a substitution variable is used in a statement, SQL*Plus requests an input value and rewrites the statement to include it. The rewritten statement is passed to the database. As a result, the database server knows nothing of the substitution variable.