问计算数学字符串中的空值，而不将其替换为0 PL/SQL

EN

DECLARE
  SUBTYPE VARIABLE_TYPE IS VARCHAR2(5);
  TYPE VARIABLE_MAP IS TABLE OF NUMBER INDEX BY VARIABLE_TYPE;

  variables  VARIABLE_MAP;
  expression VARCHAR2(4000) := 'A*(B+C)+(D*E)+F+G*(H+I)';
  v          VARIABLE_TYPE;
  e          VARCHAR2(4000);
  r          NUMBER;
BEGIN
  -- Populate the variables values
  variables('A') := 1;
  variables('B') := 2;
  variables('C') := 3;
  variables('D') := 4;
  variables('E') := 5;
  variables('F') := 6;
  variables('G') := 7;
  variables('H') := 8;
  variables('I') := 9;

  -- Replace the variables with their values:
  e := expression;
  v := variables.FIRST;
  WHILE v IS NOT NULL LOOP
    e := REPLACE( e, v, COALESCE( TO_CHAR( variables(v) ), 'NULL' ) );
    v := variables.NEXT(v);
  END LOOP;

  -- Perform the calculation
  EXECUTE IMMEDIATE 'BEGIN :1 := ' || e || '; END;' USING IN OUT r;

  -- Output the result
  DBMS_OUTPUT.PUT_LINE( r );
END;
/

150

create table dbo.Stack
(
stkID int identity(1,1) not null primary key,
stkData varchar(50) not null,
)
go

create procedure dbo.spStackPush
(
@stkData varchar(10)
)
as
begin
set nocount on
insert into Stack (stkData) values (@stkData)
if @@error <> 0 raiserror('Could not push to stack', 16, 1)
return 0
end
go

create procedure dbo.spStackPop
(
@stkData varchar(10) output
)
as
begin
set nocount on
declare @stkID int
select
@stkData = stkData,
@stkID = stkID
from dbo.Stack
where stkID = (select max(stkID) from dbo.Stack)

delete from dbo.Stack where stkID = @stkID
return 0
end
go

create procedure dbo.spStackEvaluate
(
@stkData varchar(10) output
)
as
begin
set nocount on
declare @stkLeft varchar(10)
declare @stkRight varchar(10)
declare @stkNext varchar(10)

exec dbo.spStackPop @stkData output

if @stkData = '+'
begin
exec dbo.spStackPop @stkLeft output
exec dbo.spStackPop @stkRight output

set @stkData = cast(@stkLeft as int) + cast(@stkRight as int)
end

if exists(select 1 from dbo.Stack)
begin
exec dbo.spStackPop @stkNext output
exec dbo.spStackPush @stkData
exec dbo.spStackPush @stkNext
exec dbo.spStackEvaluate @stkData output
end

return 0
end
go

-- Test script
delete dbo.Stack

declare @stkData varchar(10)

exec dbo.spStackPush '10'
exec dbo.spStackPush '+'
exec dbo.spStackPush '20'
exec dbo.spStackPush '+'
exec dbo.spStackPush '30'
exec dbo.spStackPush '40'
exec dbo.spStackPush '+'

exec dbo.spStackEvaluate @stkData output
print @stkData