How to build a new MySQL Table from 2 MySQL Tables without PHP

Question

I have 2 tables I want to merge into a third table I would like to do it purely as a MySQL query rather than selecting the rows and using PHP while() to build the third table.

Table 1 contains the following

ID Name
1  A
2
3

Table 2 contains the following

ID  Desc
10
15  B
20

I want to write a query statement to produce the following combined table, but I only want the new Desc to contain the non-blank value from Name in Table 1 or Desc in Table 2, with Table 2 getting precedence over Table 1 in the event both tables contain a non-blank

ID1 ID2 Desc
1   10  A
1   15  B
1   20  A
2   10
2   15  B
2   20
3   10
3   15  B
3   20

Is this do-able as a MySQL query I should I use a PHP method?

Thanks.

Answer 1

insert into TableThree (id1, id2, Descr)
select
    T1.id,
    T2.id,
    case LENGTH(TRIM(T2.Descr))
        when 0 then T1.Name
        else T2.Descr
    end
from TableOne T1, TableTwo T2
order by 1, 2

Answer 2

想想，你需要这个......

select t1.id as id1, t2.id as id2, if(length(t2.name), t2.desc, t1.name) as desc from t1,t2;

Answer 3

you could do it like this:

SELECT a.ID as ID1, b.ID as ID2, (CASE WHEN b.Desc is not null THEN b.Desc ELSE a.Name END) as Desc from Table1 a full join Table2;

But this is untested ... so good luck.

Regards

parascus