从源到目标评估每个字段并进行更新

Question

I am using Microsoft Sql server 2014

I have a request where i have to check if ID exists ,If ID exists then update. However client wants to evaluate each field from source and check if there are any changes in target, if there are any changes update only that field and rest of the fields should be original.

So if my original request is, Source :

ID name company salary
1 dave ABC 50000$
2 ashley XXX 50000$

Target:

ID name company salary
1 dave ABC 50000$
2 ashley XXX 50000$

Updated request: Source :

ID name company salary
1 dave ABC 80000$
2 ashley XXX 80000$

Now I have to check each column to see if there are any changes , only if any column has any change then update only that field.

target:

ID name company salary
1 dave ABC 80000$
2 ashley XXX 80000$

I cannot use hashkey/flag field as my target table does not have these fields and I cannot alter them. What is the best way to do this? Any help is appreciated

Answer 1

You can build a dinamic update query server side testing the value or you can use an update with inner join and case statement If you use mysql you can try this way

update target t
inner join source s on t.id = s.id
set case when t.name <> s.name then s.name else t.name end,
    case when t.company <> s.company then s.company else t.company end,
    case when t.salary <> s.salary then s.salary else t.salary end     

Answer 2

Thank you guys! this solution works

 MERGE testdb.dbo.targettable r
using dbo.sourcetable s
on s.id=r.id
WHEN MATCHED THEN
UPDATE 
SET column1 = CASE WHEN r.column1 <> s.column1 THEN s.column1 ELSE r.column1 END,
column2 = CASE WHEN r.column2 <> s.column2 THEN s.column2 ELSE r.column2 END,
column3 = CASE WHEN r.column3 <> s.column3 THEN s.column3 ELSE r.column3 END,
column4 = CASE WHEN r.column4 <> s.column4 THEN s.column4 ELSE r.column4 END,
column5 = CASE WHEN r.column5 <> s.column5 THEN s.column5 ELSE r.column5 END,
column6 = CASE WHEN r.column6 <> s.column6 THEN s.column6 ELSE r.column6 END

....... ;

I was looking if there is any query that can be written dynamically ie dynamically checking if any column needs update from source to target and update the target tables rather than checking each column.