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POAggregate function across two tables
 

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  1. POAggregate function across two tables
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    <p>I need for further working routine a query which calculates several functions across two (maybe more) tables. But once I import more than one table I got odd results caused by JOIN conditions. First I used that query:</p> <pre><code>SELECT sum(s.bedarf2050_kwh_a) AS bedarf_kWh_a, sum(s.bedarf2050_kwh_a)*0.2 AS netzverlust, sum(s.bedarf2050_kwh_a) + sum(s.bedarf2050_kwh_a)*0.2 AS gesamtbedarf, sum(pv.modulflaeche_qm) AS instbar_modulflaeche_qm FROM siedlungsareale_wbm s, pv_st_potenziale_gis pv WHERE s.vg_solar LIKE '%NWS 2%' AND ST_Covers(s.geom, pv.geom); </code></pre> <p>Using sum with DISTINCT returns some accurate values but only if all input values are unique. That's not a solution I can use:</p> <pre><code>SELECT SUM(DISTINCT s.bedarf2050_kwh_a) AS bedarf_kWh_a, SUM(DISTINCT s.bedarf2050_kwh_a)*0.2 AS netzverlust, SUM(DISTINCT s.bedarf2050_kwh_a) + SUM(DISTINCT s.bedarf2050_kwh_a)*0.2 AS gesamtbedarf, SUM(pv.modulflaeche_qm) AS instbar_modulflaeche_qm, (SUM(DISTINCT s.bedarf2050_kwh_a) + SUM(DISTINCT s.bedarf2050_kwh_a)*0.2)*0.01499 AS startwert_speichergroesse FROM siedlungsareale_wbm s, pv_st_potenziale_gis pv WHERE pv.vg_solar LIKE '%NWS 2%' AND ST_Covers(s.geom, pv.geom); </code></pre> <p>DISTINCT would be a proper solution if the DISTINCT refers to another column, not the column to use in the function. Or some subquery or other JOIN condition. But all I tried run in errors or false result values. </p> <p>I found some solutions using UNION dealing with aggregate function on multiple tables. But as I tried to fit the code on my query I got errors.</p> <p>For example like there: <a href="https://stackoverflow.com/questions/319262/can-sql-calculate-aggregate-functions-across-multiple-tables">Can SQL calculate aggregate functions across multiple tables?</a></p> <p>Hope someone can help me to build a working query for my task.</p> <p>[EDIT] simple example</p> <p>siedlungsareale</p> <pre><code>id | bedarf2050_kWh_a | a | b | c | vg_solar | geom ---|------------------|---|---|---|----------|----- 1 | 20 | | | | NWS 2 | xxxxx 2 | 10 | | | | NWS 2 | xxxxx 3 | 30 | | | | NWS 2 | xxxxx 4 | 5 | | | | NWS 2 | xxxxx 5 | 15 | | | | NWS 2 | xxxxx sum = 80 </code></pre> <p>pv_st_potenziale_gis</p> <pre><code>id | modulflaeche_qm | x | y | z | geom ---|------------------|---|---|---|--------- 1 | 10 | | | | xxxxx 2 | 10 | | | | xxxxx 3 | 20 | | | | xxxxx 4 | 10 | | | | xxxxx 5 | 30 | | | | xxxxx 6 | 30 | | | | xxxxx 7 | 10 | | | | xxxxx 8 | 10 | | | | xxxxx 9 | 10 | | | | xxxxx 10 | 10 | | | | xxxxx sum = 140 SELECT sum(s.bedarfxxxx) AS bedarf, sum(pv.mflaeche) As mflaeche FROM siedlungsareale s, pv_st_potenziale_gis pv WHERE s.vg_solar LIKE '%NWS 2%' AND ST_Covers(s.geom,pv.geom); </code></pre> <p>Expected correct result: </p> <pre><code>bedarf | mflaeche ---------|---------- 80 | 140 </code></pre> <p>There I would get the sum of all values for column 'bedarf' from 'siedlungsareale' and all for 'mflaeche' from 'pv_st_potenziale_gis'</p> <p>But the real calculated values of column 'bedarf' using this query are much higher caused of the CROSS JOIN condition.</p> <p>And the other query:</p> <pre><code>SELECT sum(DISTINCT s.bedarfxxxx) AS bedarf, sum(DISTINCT pv.mflaeche) As mflaeche FROM siedlungsareale s, pv_st_potenziale_gis pv WHERE s.vg_solar LIKE '%NWS 2%' AND ST_Covers(s.geom,pv.geom); </code></pre> <p>returns:</p> <pre><code>bedarf | mflaeche ---------|----------- 80 | 60 </code></pre> <p>Accurate value for 'bedarf' caused the values are unique. But for mflaeche where some values occurre several times the result is wrong. </p>
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    1. PTQuestion
    1. USCommunity
    1. USnunatak
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    1. PL
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    1. COcould you create simple example input and desired output? Yes, I can do it by myself to illustrate how you have to aggregate joined tables, but after all, it's you question.
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      1. USRoman Pekar
    2. COCan't you write something like "select someid, sum(...) from table1 t1 left join (select someid, sum(...) from table2 group by someid) t2 on t2.someid = t1.someid"? This way you group second results before joining and avoid multiplying. Using DISTINCT is clearly wrong approach.
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      1. USArvo
    3. CO"DISTINCT would be a proper solution if the DISTINCT refers to another column, not the column to use in the function." Make use of group by for the other column that you want the aggregate function to be operated on.
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      1. USAmit
 

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