Re: Update question

Markus Schaber wrote:
> Hi, Fay,
> 
> Fay Du wrote:
>> Table cost
>>
>> Id  edge_id    cost
>> 1       30         101.4
>> 2       30          null
>> 3       40          500.2
>> 4       40           null
>> 5        45          300.7
>> 6        45           null
> 
>> I want to set cost value with same edge_id by same value. The existing
>> values are calculated by calling a function (calculate edge length). I
>> can calculate the value by same function, but the function was slow. I
>> wander if I can use update statement to set the second value with same
>> edge_id. Thanks in advance for your help.
> 
> It should go like:
> 
> UPDATE cost SET edge_id = (SELECT cost FROM cost innr WHERE innr.edge_id
> = edge_id AND innr.cost is not null) WHERE cost is null;
> 
> HTH,
> Marku
> 

This is ok, but this is redundant, i guess. you should put edge_id and
cost into another table and use join to retrieve cost for each id.
put a key on edge_id, most likely a primary (unique) key.


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Gábriel Ákos
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