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I have sqlite and I query two columns from a table like this: 

result_set = conn.execute("SELECT time, MeanCurrent from MEASUREMENTS")

then, I want to put each column into a separate list, what I'm doing so far is this: 

list1 = [record[0] for record in result_set]
list2 = [record[1] for record in result_set]

The problem is that, while list1 prints the first column perfectly, list2 appears empty, while, if I remove the first line, list2 prints the second column perfectly as well!

So it's like, after the first line execution, something changes in my query but I don't know what.

Is there any way to deal with this?

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  • I don't know enough Python to express this with actual syntax, but I would define the arrays, then have a loop to iterate over the result_set and push the fields of the record into the list arrays. Commented Jan 7, 2017 at 16:52

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conn.execute() returns a cursor object. You can't iterate over a cursor more than once; when you reach the end, it won't start at the beginning again when iterating a second time. Either load all rows into a list first, or use a different technique that only needs to iterate once.

I'd use the zip() function to pair up columns:

list1, list2 = zip(*result_set)

but you could use results = list(result_set) or results = result_set.fetchall() to materialise all rows into a list first, or you could use a single loop that uses list1.append() and list2.append() to add the column values to the two lists.

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Thank you very much, spent so much time trying to figure this out!

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