在两个表之间加入

Question

table1 - doctors

+---------+--------+------+
| country |  state |  doc |
+---------+--------+------+
| india   |  AP    | 20   |
+---------+--------+------+
| india   |  TN    | 30   |
+---------+--------+------+
| india   |  KA    | 10   |
+---------+--------+------+
| US      |  LA    | 30   |
+---------+--------+------+
| US      |  CA    | 10   |
+---------+--------+------+
| US      |  NY    | 50   |
+---------+--------+------+

table2 - engineers

+---------+--------+-------+
| country |  state |  engg |
+---------+--------+-------+
| india   |  AP    | 100   |
+---------+--------+-------+
| india   |  TN    | 400   |
+---------+--------+-------+
| india   |  KA    | 250   |
+---------+--------+-------+
| US      |  LA    | 140   |
+---------+--------+-------+
| US      |  CA    | 120   |
+---------+--------+-------+
| US      |  NY    | 150   |
+---------+--------+-------+

Desired output:

+---------+------+-------+
| country |  doc |  engg |
+---------+------+-------+
| india   | 60   | 750   |
+---------+------+-------+
| US      | 90   | 410   |
+---------+------+-------+

I tried with the below query but am getting more count of docs and engg. Someone please correct me..

select country, sum(a.doc), sum(b.engg) 
  from table1 a join table2 b on (a.country = b.country) 

Answer 1

I think your problem is that you are getting a cross-product of both the tables with these set of values.

Try using:

tableA NATURAL JOIN tableB.

Answer 2

You can use UNION ALL

SELECT
    country,
    SUM(doc) AS doc,
    SUM(engg) AS engg
FROM
    (SELECT
        country,
        doc,
        0 AS engg
     FROM
        doctors
     UNION ALL
     SELECT
        country,
        0,
        engg
     FROM
        engineers
    ) a
GROUP BY
    country

Answer 3

You need to group by country.

select a.country, sum(docSum), sum(enggSum) from
  (select country, sum(doc) docSum from doctors) a
inner join
  (select country, sum(engg) enggSum from engineers)
on a.country = b.country
group by a.country