IN和IF在PL/SQL運營商

Question

我試圖做（在PL/SQL）

if ((var1, var2) in (select number1, number2 from.......)) then 
.... 
end if; 

爲什麼這個不行？ 如何做纔是正確的事情？

Answer 1

答案是，在PL/SQL，你必須閱讀（select）的東西到變量，然後在IF語句中使用它。你可以用各種方式做到這一點，但你不能在IF條款中做到這一點。 Chorel的回答在這方面非常有創意，他對這個答案值得讚賞。

你也可以只做到

declare 
    l_count number; 
    var1 number := 1; -- or whatever the number 
    var2 number := 2; 
begin 
    select count(*) 
    into l_count 
    from mytable 
    where number1 = var1 and number2 = var2; 
    if l_count > 0 then 
    ... the row exists 
    end if; 
end; 

但是下面不起作用

if (select count(*) from mytable where (number1,number2) in (1,2)) > 0 then -- WRONG 
    ... 
end if; 

如果你想使用in功能，你不得不求助於表dual

where (number1, number2) in (select var1, var2 from dual); 

像這樣

declare 
    l_count number; 
    var1 number := 1; -- or whatever the number 
    var2 number := 2; 
begin 
    select count(*) 
    into l_count 
    from mytable 
    where (number1, number2) in (select var1, var2 from dual); 
    if l_count > 0 then 
    ... 
    end if; 
end; 

Answer 2

試試這個：

declare 
    l_exist number(1); 
    var1 ... 
    var2 ... 
begin 
    --obtain var1 & var2 
    -- ... 
    select 
    case 
     when exists(select1 from ... 
        where number1 = var1 and number2 = var2) then 1 
     else 0 
    end into l_exist 
    from dual; 

    if l_exist = 1 
    then 
    -- do what you want here 
    end if; 
end;