比较两个数据表并获取C＃中的差异行

Question

Here is an example, let say I have two datatables.

Table_1
id     name     age
===================
1      john     20
2      henry    25
3      sam      18
4      tom      30


Table_2
id     name     age
===================
1      john     20
2      henry    26     <=== Edited Row
3      sam      19     <=== Edited Row 
4      tom      30

Those two tables are in diffenrence database ( with same schema ).
I loaded them into two DataTable and find difference rows by using Except like

dt_Table_1.AsEnumerable().Except(dt_Table_2.AsEnumerable())

Using Except returns only newly inserted rows but not Edited Rows .
I just want to get the Edited Rows.
Above tables are just examples, my real data has many rows, so I have to consider about the performance.That's why I don't want to do with looping for each row.
Is there any better way to do it ?

Answer 1

you can get the changed rows from datatable and add them to your result.

DataTable changedRecordsTable = dataTable1.GetChanges();//get changed rows

dt_Table_1.AsEnumerable().Except(dt_Table_2.AsEnumerable()).Union(changedRecordsTable.AsEnumerable())

you should do this before calling accept changes and keep in mind that this compares the hash for values which is different for two different instances and hence result will have all rows from all datatables(ie duplicates are not removed)

Answer 2

You can simple construct a query that will give you the rows that changed:

select * from table_1 inner join table_2 on table_1.id=table_2.id and table_1.age<>table_2.age

However if you add or delete rows, they will not appear, you can run

select * from table_1 where id not in (select id from table_2)

To get all those deleted from table_1 and

select * from table_2 where id not in (select id from table_1)

to get the rows deleted from table_2

You can combine them all in a single query and put a status (deleted or edited) by running this:

select table_1.id, table_1.name, table_1.age, 'edited' as rowstatus from table_1 inner join table_2 on table_1.id=table_2.id and table_1.age<>table_2.age
union
select id, name, age, 'deleted table_1' as rowstatus from table_1 where id not in (select id from table_2)
union
select id, name, age, 'deleted from table_2' as rowstatus from table_2 where id not in (select id from table_1)