在两个表之间选择不常见的记录-MySQL

Question

I have two tables, table A and table B with the same column names. I want to fetch those records which are not present in table A but present in table B.

Thanks in advance.

Answer 1

使用左联接

Select * from tableb left join tablea on tableb.column = tablea.coulmn where tablea.column is null 

Answer 2

Some databases support except or minus . But not MySQL. I would recommend not exists :

select b.*
from b
where not exists (select 1
                  from a
                  where a.col1 = b.col1 and a.col2 = b.col2 and . . .
                 );

Note that this will not work if any columns have NULL values.

If you need to handle NULL s, you could use (not a.col1 <=> b.col1) and (not a.col2 <=> b.col2) . . . (not a.col1 <=> b.col1) and (not a.col2 <=> b.col2) . . . . Or, you could use aggregation:

select col1, col2, . . .
from ((select a.*, 1 as is_a, 0 as is_b
       from a
      ) union all
      (select b.*, 0, 1
       from b
      ) 
     ) ab
group by col1, col2, . . .
having max(is_a) = 0 and max(is_b) = 1;

Answer 3

Suppose the rows are same if their primary keys are same (for example, id field). Than you can:

select id from b where id not in (select id from a)

If your tables has no primary keys or they do not match - you can alter the query to your tables structure.