如何为PL/SQL块的表达式中的变量赋值? [英] how to assign value to variable in expression for a PL/SQL block?

问题描述

运行此脚本时，它在此语句no1:=(no1+no2)-(no2:=no1);

When I run this script it returns error in this statement no1:=(no1+no2)-(no2:=no1);

declare
    no1 number(3):=31;
    no2 number(3):=34;
begin
    dbms_output.put_line('Before swap');
    dbms_output.put_line('No1 : '||no1||'  No2 : '||no2 );
--  no1:=(no1+no2)-(no2:=no1);  generate error
    dbms_output.put_line('After swap');
    dbms_output.put_line('No1 : '||no1||'  No2 : '||no2 );
end;

推荐答案

除了在PL/SQL中使用xor技巧外，您还可以简单地使用SQL语句

In addition to using the xor trick in PL/SQL, you can simply use a SQL statement

DECLARE
  a number := 17;
  b number := 42;
BEGIN
  SELECT a, b
    INTO b, a
    FROM dual;
  dbms_output.put_line( 'a = ' || a );
  dbms_output.put_line( 'b = ' || b );
END;

在不使用临时变量的情况下交换两个变量

which swaps the two variables without using a temp variable

SQL> ed
Wrote file afiedt.buf

  1  DECLARE
  2    a number := 17;
  3    b number := 42;
  4  BEGIN
  5    SELECT a, b
  6      INTO b, a
  7      FROM dual;
  8    dbms_output.put_line( 'a = ' || a );
  9    dbms_output.put_line( 'b = ' || b );
 10* END;
SQL> /
a = 42
b = 17

PL/SQL procedure successfully completed.

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