sql选择更新多列并在更新前检查是否不为空

Question

I have two tables.
Table1 structure NOT NULL.
Table2 some value NULL.
I want update table2 to table1 ,
I want when select value if null don't update and skip next column have value to update.

My Table

table1      value(table1)      table2       value(table2)
t1ID        1234               t2ID         1234
t1Name      Bear               t2Name       null
t1Adress    87/25              t2Adress     99/77
t1Tel       01254798535        t2Tel        null

My Code

UPDATE table1
SET t1Name = (SELECT t2Name
    FROM table2
    WHERE t2Name IS NOT NULL
    ),
    t1Adress = (SELECT t2Adress
    FROM table2
    WHERE t2Adress IS NOT NULL
    ),
    t1Tel = (SELECT t2Tel
    FROM table2
    WHERE t2Tel IS NOT NULL
    )
FROM table1,table2
WHERE t1ID = '1234' AND t2ID ='1234'

When I execute I get error:

SQL error : Msg 512, Level 16, State 1, Line 1 Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression. The statement has been terminated.

How can I fix it?

Answer 1

I think you intend:

UPDATE t1
    SET t1Name = COALESCE(t2.t2Name, t1.t1Name),
        t1Adress = COALESCE(t2.t2Adress, t1.t1Adress),
        t1Tel = COALESCE(t2.t2Tel, t1.t2Tel)
    FROM table1 t1 JOIN
         table2 t2
         ON t1.t1id = t2.t2id
    WHERE t1.t1ID = 1234;

Note that I removed the single quotes on '1234' . Id s are usually numbers so they should be compared to numbers.

Your code fails because you are using subqueries instead of the values from the join . You seem to have multiple rows in table2 , so you are getting the subquery returned more than one row error.

Answer 2

The following query replaces the null values with table1 values and updates the rest from table2 values

UPDATE T1 SET T1.t1Name = IsNull(T2.t2Name,T1.t1Name),
              T1.t1Adress = IsNull(T2.t2Adress,T1.t1Adress),
              T1.t1Tel = IsNull(T2.t2Tel,T1.t1Tel)
        FROM table1 TI
                INNER JOIN table2 T2 ON T1.t1ID = T2.t2ID

Try the following select query to check your result

SELECT T1.t1Name,IsNull(T2.t2Name,T1.t1Name),T1.t1Adress,IsNull(T2.t2Adress,T1.t1Adress),T1.t1Tel,IsNull(T2.t2Tel,T1.t1Tel)
        FROM table1 TI
                INNER JOIN table2 T2 ON T1.t1ID = T2.t2ID