查询以从一个表中获取一个条件的总和，然后将其添加到另一张表中的相同条件中

Question

What I have is two tables;

heli_acft :

• acft_id
  
• acft_reg
  
• acft_hours

heli_flt :

• flt_id
  
• flt_acft
  
• flt_colhr

acft_id correlates to flt_acft .

I want to get the total sum of all flt_colhr of each flt_acft in the table, and then add that figure to the value of acft_hours per acft_id .

The result will then be displayed as a <?php echo data[???] ?> in a table.

Any ideas on how I could do this?

Answer 1

Join the tables and calculate the sum. I use a LEFT JOIN to get a zero result for aircraft that have no flights.

SELECT acft_id, acft_hours + IFNULL(SUM(flt_colhr), 0) AS total_colhr
FROM heli_acft 
LEFT JOIN heli_flt ON acft_id = flt_acft
GROUP BY acft_id

Answer 2

Assuming that acft_id is a unique idenfifier in flt_acft table...

Here is one approach to returning the specified resultset, adding the total of "hours" (from heli_flt to the "hours" from heli_acft :

 SELECT a.acft_id
      , a.acft_hours
      , IFNULL(f.flt_hours,0)
      , a.acft_hours + IFNULL(f.flt_hours,0) AS total_hours
   FROM heli_acft a
   LEFT
   JOIN ( SELECT SUM(h.flt_colhr) AS flt_hours
               , h.flt_acft
            FROM heli_flt h
           GROUP BY h.flt_acft
        ) f
     ON f.flt_acft = a.acft_id

The inline view calculates f calculates the sum of the hours from heli_flt for each flt_acft . A JOIN to heli_acft to get the acft_hours , and we simply add the values of the two columns. We use an "outer" join so we can return rows from heli_acft that don't have any related rows in heli_flt , and use an IFNULL() function to replace a NULL value with a zero.