MySQL使用CAST和SUM以及JOIN

Question

I have the following 3 MySQL queires:

-1-

 SELECT CAST(SUM(revenue) AS CHAR) revenue FROM PA
 WHERE site_id = 2 AND data_date BETWEEN '2016-01-01' AND '2016-01-01';

-2-

SELECT CAST(SUM(revenue) AS CHAR) revenue FROM PB
 WHERE site_id = 2 AND data_date BETWEEN '2016-01-01' AND '2016-01-01';

-3-

SELECT CAST(SUM(revenue) AS CHAR) revenue FROM PC
 WHERE site_id = 2 AND data_date BETWEEN '2016-01-01' AND '2016-01-01';

each one will give me the revenue only from the queried table. Problem is i want to get total revenue from all 3 tables, any idea how can i join them? my last attempt was:

SELECT
    PA.CAST (SUM(PA.revenue) AS CHAR) revenue,
    PB.CAST (SUM(PB.revenue) AS CHAR) revenue,
    PC.CAST (SUM(PC.revenue) AS CHAR) revenue
FROM
    PA
INNER JOIN PB ON PA.site_id = PB.site_id
INNER JOIN PC ON PA.site_id = PC.site_id

but i have error in my syntax here...any idea how to do it?

ERROR:

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'AS CHAR) revenue, PB.CAST(SUM(PC' at line 1

Answer 1

Don't qualify the function with a table alias.

This is wrong...

  PA.CAST(SUM(revenue))
  ^^^

Qualify the reference to the column...

  CAST(SUM(PA.revenue))
           ^^^

That's the syntax error.

But I don't think you want to join those tables... there's potential there for producing a cross product (semi-Cartesian product) of those tables.

If no rows are returned from one of the tables, then the query will return zero rows. Or, if more than one row is returned from one of the tables for the same site_id , that's going to produce "duplicate" rows, and the SUM will be inflated.

---

Without knowing what you are attempting to achieve...

Given examples of working queries, we can propose something like this, though there may be a more efficient way to achieve an equivalent result.

  SELECT SUM(v.revenue) AS revenue
    FROM ( 
           ( 
             SELECT SUM(PA.revenue) AS revenue
               FROM PA
              WHERE PA.site_id = 2 
                AND PA.data_date BETWEEN '2016-01-01' AND '2016-01-01'
           )
           UNION ALL
           (
             SELECT SUM(PB.revenue) AS revenue
               FROM PB
              WHERE PB.site_id = 2 
                AND PB.data_date BETWEEN '2016-01-01' AND '2016-01-01'
           )
           UNION ALL
           (
             SELECT SUM(PC.revenue) AS revenue
               FROM PC
              WHERE PC.site_id = 2 
                AND PC.data_date BETWEEN '2016-01-01' AND '2016-01-01'
           )
         ) v

Answer 2

Since each query will return a 1-row, 1-column result, you can just do a Cartesian join, ie don't join.

SELECT a.revenue AS a_revenue
     , b.revenue AS b_revenue
     , c.revenue AS c_revenue
  FROM ( SELECT CAST(SUM(revenue) AS CHAR) revenue
           FROM PA
          WHERE site_id = 2
            AND data_date BETWEEN '2016-01-01' AND '2016-01-01'
       ) a
     , ( SELECT CAST(SUM(revenue) AS CHAR) revenue
           FROM PB
          WHERE site_id = 2
            AND data_date BETWEEN '2016-01-01' AND '2016-01-01'
       ) b
     , ( SELECT CAST(SUM(revenue) AS CHAR) revenue
           FROM PC
          WHERE site_id = 2
            AND data_date BETWEEN '2016-01-01' AND '2016-01-01'
       ) c

If you just want the total value, rather than the 3 individual values, use UNION ALL :

SELECT CAST(SUM(revenue) AS CHAR) revenue
  FROM ( SELECT revenue
           FROM PA
          WHERE site_id = 2
            AND data_date BETWEEN '2016-01-01' AND '2016-01-01'
         UNION ALL
         SELECT revenue
           FROM PB
          WHERE site_id = 2
            AND data_date BETWEEN '2016-01-01' AND '2016-01-01'
         UNION ALL
         SELECT revenue
           FROM PC
          WHERE site_id = 2
            AND data_date BETWEEN '2016-01-01' AND '2016-01-01'
       ) x