SQL Server：是列值为空从另一个表中获得列

Question

我有两个表。如果在表格中的百分比为null，则我想看看它在表B中

SELECT 
    t.id, 
    CASE 
     WHEN t.percentage IS NULL 
     THEN (SELECT percentage FROM test2 AS s WHERE s.id=t.id) 
     ELSE t.percentage 
    END AS percentage 
FROM 
    [project_percentage] t 

Answer 1

这应做到：

SELECT t.id, COALESCE(t.percentage, s.percentage) AS percentage 
FROM project_percentage t 
LEFT OUTER JOIN 
test2 AS s 
ON s.id = t.id;