多列更新

Question

我必須在過程中執行以下更新行。我可以在一行中更新它嗎？這裏只有一張桌子。

UPDATE magic_table SET first_col=0,last_col=my_value where first_col is not null; 
    UPDATE magic_table SET second_col=0,last_col=my_value where second_col is not null; 
    UPDATE magic_table SET third_col=null,last_col=my_value where third_col is not null; 

如果是這樣，它會給我們任何性能改進？

Answer 1

update magig_table 
    set first_col = nvl2(first_col , 0, first_col), 
     second_col = nvl2(second_col, 0, second_col), 
     third_col = nvl2(third_col , 0, third_col), 
     last_col = my_value 
    where first_col is not null or 
     second_col is not null or 
     third_col is not null; 

Answer 2

試試這個：

update magig_table 
set first_col = case when first_col is not null then 0 end, 
    second_col = case when second_col is not null then 0 end, 
    third_col = null, 
    last_col = my_value 
where coalesce(first_col,second_col,third_col) is not null; 

這種方式是更好的性能則nvl2使用。第三列無論如何都是空的，所以沒有必要檢查它。