[mythtv-users] Possibly OT: Merging Tables, NO duplicates.

[R. G. Newbury]

  I am having a problem which I am sure has been addressed by someone 
before now, and I don't wish to waste time re-inventing the wheel,

I have a small (presently command-line controlled) sqlite program to 
keep track of time usage. It runs on 3 different physical computers. I 
need to merge the entries, *without duplication*. All three units run 
the same app and the tables are the same. But I want the entries I make 
on the laptop and/or the Nokia tablet to end up merged into the 'master' 
on the desktop.

At the moment I cannot see how I can select 'distinct' from 2 tables, so
I *think* to do this, I will need to copy each table onto the 'master 
machine' then,

presuming each row on each copy of the table to have a unique primary 
key based on the entry values;
and at  'merge time',
b) update seriatim from all the various instances into a necessarily 
large temporary table number 1; then,
c) update into temporary table 2, using a 'select distinct' to obtain 
the unique entries; and finally,
d) copy the resulting temporary table 2, back over the orginal table, in 
each case.


So if table A has rows 'a,b.c' and table B has 'a,b,c,d' and table C has 
'a,b,c,e', temp 1 will have 'a,a,a,b,b,b,c,c,c,d,e' and table 2 will end 
up with 'a,b,c,d,e'...and will be copied over A, B and C.

Is this the way to do it, or am I missing something really easy, such as 
a horribly complex 'select....join' statement. Note that the schema of 
all of these tables is exactly the same.

(And the answer to this has some relevance to updating/merging different 
instances of mythtv tables....such as moving a mythfilldatabase update 
from one machine to another without replacing the entire table.)

Geoff
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