如果更新值爲null

Question

我有這樣的查詢（在一個函數）不更新列：

UPDATE some_table SET 
    column_1 = param_1, 
    column_2 = param_2, 
    column_3 = param_3, 
    column_4 = param_4, 
    column_5 = param_5 
WHERE id = some_id; 

哪裏param_x是我的函數的參數。有沒有辦法不更新這些列，參數爲NULL？例如 - 如果param_4和param_5是NULL，則只更新前三列併爲column_4和column_5保留舊值。

我現在做的方式是：

SELECT * INTO temp_row FROM some_table WHERE id = some_id; 

UPDATE some_table SET 
    column_1 = COALESCE(param_1, temp_row.column_1), 
    column_2 = COALESCE(param_2, temp_row.column_2), 
    column_3 = COALESCE(param_3, temp_row.column_3), 
    column_4 = COALESCE(param_4, temp_row.column_4), 
    column_5 = COALESCE(param_5, temp_row.column_5) 
WHERE id = some_id; 

有沒有更好的辦法？

Answer 1

下降SELECT語句，沒有必要，只是使用當前值：

UPDATE some_table SET 
    column_1 = COALESCE(param_1, column_1), 
    column_2 = COALESCE(param_2, column_2), 
    column_3 = COALESCE(param_3, column_3), 
    column_4 = COALESCE(param_4, column_4), 
    column_5 = COALESCE(param_5, column_5) 
WHERE id = some_id; 

Answer 2

此外，爲了避免空更新：

UPDATE some_table SET 
    column_1 = COALESCE(param_1, column_1), 
    column_2 = COALESCE(param_2, column_2) 
    ... 
WHERE id = some_id; 
AND (param_1 IS DISTINCT FROM column_1 OR 
     param_2 IS DISTINCT FROM column_2 OR 
     ... 
    ); 

Answer 3

絕招，謝謝Przemek，弗蘭克&歐文！

我建議對Erwin的答案進行小修改以避免空的更新。如果任何參數爲null（意思是：「使用舊值」），即使行值沒有更改（第一次更新後），每次更新該行。

通過添加 「param_x IS NOT NULL」，我們避免了空更新：

UPDATE some_table SET 
    column_1 = COALESCE(param_1, column_1), 
    column_2 = COALESCE(param_2, column_2), 
    ... 
WHERE id = some_id 
AND (param_1 IS NOT NULL AND param_1 IS DISTINCT FROM column_1 OR 
     param_2 IS NOT NULL AND param_2 IS DISTINCT FROM column_2 OR 
    ... 
);