Having trouble with left join SQL in SQLite - sql

Question

Short background: I have an SQLite database, a couple of gb in size and growing. It contains a bunch of very simple tables. Each table consists of a 64-bit integer primary index field (TStamp) and a value field (Val). The field TStamp is actually an long-int representation of a date-time. The tables have widely varying row-counts and somewhat variable content types, but that shouldn't matter. A master table (tbIndDate) holds a full range of dates, has the same primary index (TStamp) as the other tables, and holds human-readable date-time in its Val field. For instance,
The master index table, named tbIndDate:
TStamp Val
634082688000000000 5/1/2010 0:00:00
634082691000000000 5/1/2010 0:05:00
634082694000000000 5/1/2010 0:10:00
634082697000000000 5/1/2010 0:15:00
etc etc
A sample table for automation tag 6FI1.PV, named tb6FI1%PV:
TStamp Val
634085793000000000 41.7
634085796000000000 42.83
634085799000000000 41.44
634085802000000000 40.43
634085805000000000 39.78
etc etc
Getting data into the tables is handled by a little vb.net program, and when a new automation tag is added to the capture list then the program creates a new table using the automation tag name, and begins populating it. That all works real slick.
OK. I've started building a tool for getting data out of the database. It works great for inner joins:
SELECT [tbIndDate].[Val] AS 'Timestamp',[tb6FI1%PV].[Val] AS '6FI1.PV',
[tb6FI34%PV].[Val] AS '6FI34.PV',[tb6AI32%PV].[Val] AS '6AI32.PV'
FROM [tbIndDate],[tb6FI1%PV],[tb6FI34%PV],[tb6AI32%PV]
WHERE [tbIndDate].[TStamp]=[tb6FI1%PV].[TStamp]
AND [tbIndDate].[TStamp]=[tb6FI34%PV].[TStamp]
AND [tbIndDate].[TStamp]=[tb6AI32%PV].[TStamp];
This returns:
Timestamp 6FI1.PV 6FI34.PV 6AI32.PV
1/1/2013 0:00:00 42.4679 1.499 0.8439
1/1/2013 0:05:00 40.3628 1.5048 0.8435
1/1/2013 0:10:00 38.2652 1.5028 0.8436
1/1/2013 0:15:00 37.8582 1.5029 0.8436
Yay! :)
I've also gotten some averaging and time-interval queries working.
However, because tag data is not all available for all dates, I'd like to create the option to list all dates in the master index even if some of the tag tables do not have matching data.
A SELECT query with a left outer join, in other words. Everyone knows that. The data might look like:
Timestamp 6FI1.PV 6FI34.PV 6AI32.PV
1/1/2013 0:00:00 42.4679 1.499 NULL
1/1/2013 0:05:00 40.3628 1.5048 NULL
1/1/2013 0:10:00 38.2652 NULL NULL
1/1/2013 0:15:00 37.8582 NULL 0.8436
Trouble is, none of the SQL I've tried has worked. Here's one that didn't go:
SELECT [tbIndDate].[Val] AS 'Timestamp',[tb6FI1%PV].[Val] AS '6FI1.PV',
[tb6FI34%PV].[Val] AS '6FI34.PV'
FROM [tbIndDate],[tb6FI1%PV],[tb6FI34%PV]
LEFT JOIN [tbIndDate] ON [tbIndDate].[TStamp]=[tb6FI1%PV].[TStamp]
LEFT JOIN [tbIndDate] ON [tbIndDate].[TStamp]=[tb6FI34%PV].[TStamp];
The error was "SQL error or missing database, ambiguous column name: tbIndDate.Val"
I've tried copying the syntax from several examples, but none are exactly the same and my attempts fail.
Am I doing the aliases wrong? The square brackets to accommodate special characters in table names? I'm a complete SQL beginner, so don't hold back with the advice.

Answer 1

It looks like the problem is that you're trying to join [tbIndDate] several times. Try this:
SELECT [tbIndDate].[Val] AS 'Timestamp',[tb6FI1%PV].[Val] AS '6FI1.PV',
[tb6FI34%PV].[Val] AS '6FI34.PV'
FROM [tbIndDate]
LEFT JOIN [tb6FI1%PV] ON [tbIndDate].[TStamp]=[tb6FI1%PV].[TStamp]
LEFT JOIN [tb6FI34%PV] ON [tbIndDate].[TStamp]=[tb6FI34%PV].[TStamp];