Sql query for updating database if value is not null?

I am having a table which has about 17 fields. I need to perform frequent updates in this table. But the issue is each time I may be updating only a few fields. Whats the best way to write a query for updating in such a scenario? I am looking for an option in which the value gets updated only if it is not null.

For example I have four fields in database Say A,B,C,D. User updates the value of say D. All other values remains the same. So I want an update query which updates only the value of D keeping the others unaltered. SO if i put a,b and c as null and d开发者_开发百科 with the value supplied by user I want to write an update query which only updates the value of d as a,b and c is null. Is it something achievable?

I am using SQLite database.

Could someone please throw some light into it?

Without knowing your database it's tough to be specific. In SQL Server the syntax would be something like ...

UPDATE MyTable 
SET 
        Field1 = IsNull(@Field1, Field1),
        Field2 = IsNull(@Field2, Field2),
        Field3 = IsNull(@Field3, Field3)
WHERE 
     <your criteria here>

EDIT

Since you specified SQLLite ...replace my IsNull function with COALESCE() or alternately look at the IfNull function.

Posting a SQL Server solution with 2 tables for posterity. Query joins two tables and updates the values that are present. Otherwise original value is maintained.

tables = table1, table2 each having field1 and field2

update t1 WITH (ROWLOCK)
set T1.Field2 = ISNULL(T2.Field2,T1.Field2)
from Table1 T1 Join Table2 T2 
    ON T1.Field1 = T2.Field1