Clever Geek Handbook

How do I assign a value to a variable in an expression for a PL / SQL block?

When I run this script it returns an 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;
+3


source to share


4 answers


Apart from using the xor trick in PL / SQL, you can simply use the 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;


which replaces two variables without using a temporary 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.
+9


source


Actually, you can also replace two numbers without a tempo number using the Swap XOR Algorithm (but you still have 3 commands):

declare
  no1 number(3):=31;
  no2 number(3):=34;
begin
  dbms_output.put_line('Before swap');
  dbms_output.put_line('No1 : '||no1||'  No2 : '||no2 );

  n1 := (n1 + n2) - bitand(n1,n2) * 2;
  n2 := (n2 + n1) - bitand(n2,n1) * 2;
  n1 := (n1 + n2) - bitand(n1,n2) * 2;

  dbms_output.put_line('After swap');
  dbms_output.put_line('No1 : '||no1||'  No2 : '||no2 );
end;


As for how bitwise xor in plsql see here

IMHO one should avoid one-liners in real programs, they are interested in writing, but hell to maintain them ...

+3


source


You cannot perform multiple assignments in the same expression so that they continue to generate errors. Instead, I suggest you define a temporary variable and use it for your swap operation, for example:

declare
  no1 number(3):=31;
  no2 number(3):=34;
  temp number;
begin
  dbms_output.put_line('Before swap');
  dbms_output.put_line('No1 : '||no1||'  No2 : '||no2 );
  --  no1:=(no1+no2)-(no2:=no1);  generate error
  temp := no1;
  no1 := no2;
  no2 : temp;
  dbms_output.put_line('After swap');
  dbms_output.put_line('No1 : '||no1||'  No2 : '||no2 );
end;
+2


source


You can declare an additional procedure with the following login parameters:

PROCEDURE swap(a IN OUT NUMBER, b IN OUT NUMBER) is
    buff NUMBER;
BEGIN
    buff := a;
    a := b;
    b := buff;
END swap;

and use it like this:

swap(a, b);
+1


source






More articles:


All Articles