compare two tables with different field names in SQL

Question

What is the best way to compare data values in 2 different tables having same primary key in both tables?

Can anyone suggest the best method for this?

Answer 1

If you want to compare data values, there are two levels;

1. you could have rows in one table that don't exist in another. Here you will need to do two left join queries with each of the tables on one side.

2. for the records that are in common, you will need to compare the fields one by one. There is unfortunately on easy way. The other way is to do a checksum across the whole row.

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Answer 2

The usual way to compare two tables is a full outer join , like:

select  coalesce(t1.pk, t2.pk) as Key
,       case 
        when t1.pk is null then 'Not found in Table1'
        when t2.pk is null then 'Not found in Table2'
        else 'Different'
        end as Reason
from    Table1 as t1
full outer join
        Table2 as t2
on      t1.pk = t2.pk
where   t1.pl is null 
        or t2.pk1 is null 
        or t1.col1 <> t2.col1
        or t1.col2 <> t2.col2
        or t1.col3 <> t2.col3
        ...

Nullable columns require extra logic. Assuming that no row contains the value <<NULL>> , you could:

        or IsNull(t1.col4,'<<NULL>>') <> IsNull(t2.col4,'<<NULL>>')

Answer 3

Try with binary_checksum function, something like this:

declare @Table1 table (Id int identity(1,1), Param1 varchar(10), Param2 int)
declare @Table2 table (Id int identity(1,1), Param1 varchar(10), Param2 int)

insert into @Table1 (Param1, Param2) select 'A', 1
insert into @Table2 (Param1, Param2) select 'A', 1

select t1.*, t2.*
from @Table1 t1 full join @Table2 t2 on (t1.Id = t2.Id)
where binary_checksum(t1.Id, t1.Param1, t1.Param2) <> binary_checksum(t2.Id, t2.Param1, t2.Param2)

The query returns records, that are just in one table and not in another. The query also returns records, that are in both tables (using primary key), but the other columns are different.

Edit - what do you mean with different field names? If both tables have different fields, than off course they are different...