In had a rather large error in my previous question

[select earliest date from multiple rows](https://stackoverflow.com/questions/13433263/sql-select-earliest-date-for-multiple-rows)

The answer by horse\_with\_no\_name returns a perfect result, and I am hugely appreciative, however I got my own initial question wrong so I really apologise; if you look at the table below;

```

circuit_uid  |customer_name     |rack_location  |reading_date   | reading_time | amps | volts  |  kw  | kwh | kva  |  pf  |  key 
--------------------------------------------------------------------------------------------------------------------------------------
cu1.cb1.r1    | Customer 1       | 12.01.a1      | 2012-01-02   | 00:01:01     | 4.51 | 229.32 | 1.03 |  87 | 1.03 | 0.85 |    15
cu1.cb1.r1    | Customer 1       | 12.01.a1      | 2012-01-02   | 01:01:01     | 4.18 | 230.3  | 0.96 |  90 | 0.96 | 0.84 |    16
cu1.cb1.r2    | Customer 1       | 12.01.a1      | 2012-01-02   | 00:01:01     | 4.51 | 229.32 | 1.03 |  21 | 1.03 | 0.85 |    15
cu1.cb1.r2    | Customer 1       | 12.01.a1      | 2012-01-02   | 01:01:01     | 4.18 | 230.3  | 0.96 |  23 | 0.96 | 0.84 |    16
cu1.cb1.s2    | Customer 2       | 10.01.a1      | 2012-01-02   | 00:01:01     | 7.34 | 228.14 | 1.67 | 179 | 1.67 | 0.88 | 24009
cu1.cb1.s2    | Customer 2       | 10.01.a1      | 2012-01-02   | 01:01:01     | 9.07 |  228.4 | 2.07 | 182 | 2.07 | 0.85 | 24010
cu1.cb1.s3    | Customer 2       | 10.01.a1      | 2012-01-02   | 00:01:01     | 7.34 | 228.14 | 1.67 | 121 | 1.67 | 0.88 | 24009
cu1.cb1.s3    | Customer 2       | 10.01.a1      | 2012-01-02   | 01:01:01     | 9.07 |  228.4 | 2.07 | 124 | 2.07 | 0.85 | 24010
cu1.cb1.r1    | Customer 3       | 01.01.a1      | 2012-01-02   | 00:01:01     | 7.32 | 229.01 | 1.68 | 223 | 1.68 | 0.89 | 48003 
cu1.cb1.r1    | Customer 3       | 01.01.a1      | 2012-01-02   | 01:01:01     | 6.61 | 228.29 | 1.51 | 226 | 1.51 | 0.88 | 48004
cu1.cb1.r4    | Customer 3       | 01.01.a1      | 2012-01-02   | 00:01:01     | 7.32 | 229.01 | 1.68 | 215 | 1.68 | 0.89 | 48003 
cu1.cb1.r4    | Customer 3       | 01.01.a1      | 2012-01-02   | 01:01:01     | 6.61 | 228.29 | 1.51 | 217 | 1.51 | 0.88 | 48004

```

As you can see each customer now has multiple circuits. So the result would now be the sum of each of the earliest kwh readings for each circuit per customer, so the result in this table would be;

```
customer_name | kwh(sum)
--------------+-----------
customer 1    | 108      (the result of 87 + 21)  
customer 2    | 300      (the result of 179 + 121)  
customer 3    | 438      (the result of 223 + 215)   

```

There will be more than 2 circuits per customer and the readings can happen at varying times, hence the need for the 'earliest' reading.

Would anybody have any suggestions for the revised question?

PostgreSQL 8.4 on CentOs/Redhat.