I'm trying to check whether a variable exists in an SQLite3 db. Unfortunately I can not seem to get it to work. The airports table contains 3 colums, with ICAO as the first column.
if c.execute("SELECT EXISTS(SELECT 1 FROM airports WHERE ICAO='EHAM')") is True:
print("Found!")
else:
print("Not found...")
The code runs without any errors, but the result is always the same (not found).
What is wrong with this code?
Try this instead:
c.execute("SELECT EXISTS(SELECT 1 FROM airports WHERE ICAO='EHAM')")
if c.fetchone():
print("Found!")
else:
print("Not found...")
Return value of cursor.execute
is cursor (or to be more precise reference to itself) and is independent of query results. You can easily check that:
>>> r = c.execute("SELECT EXISTS(SELECT 1 FROM airports WHERE ICAO='EHAM')")
>>> r is True
False
>>> r is False
False
>>> r is None
False
>>> r is c
True
From the other hand if you call cursor.fetchone
result tuple or None if there is no row that passes query conditions. So in your case if c.fetchone():
would mean one of the below:
if (1, ):
...
or
if None:
...
Let's prepare a database to test it.
import sqlite3
c = sqlite3.connect(":memory:")
c.execute("CREATE TABLE airports (ICAO STRING, col2 STRING, col3 STRING)")
c.execute("INSERT INTO airports (ICAO, col2, col3) VALUES (?, ?, ?)", ('EHAM', 'value2', 'value3'))
Since your SELECT 1 FROM airports WHERE ICAO = 'EHAM'
already serves the purpose of checking existence, let's use it directly, without the redundant SELECT EXISTS()
if c.execute("SELECT 1 FROM airports WHERE ICAO = 'EHAM'").fetchone():
print("Found!")
else:
print("Not found...")
the result is
Found!
Let's check a non-existent case
if c.execute("SELECT 1 FROM airports WHERE ICAO = 'NO-SUCH'").fetchone():
print("Found!")
else:
print("Not found...")
the result is
Not found...
If you just want to fix your code, you can try
if c.execute("SELECT EXISTS(SELECT 1 FROM airports WHERE ICAO = 'EHAM')").fetchone() == (1,):
print("Found!")
else:
print("Not found...")
the result is
Found!
Thanks for the answer from zero323, although the code snippet is wrong, as fetchone()
does not return True or False. It only returns 1 for True and 0 for False. (binary) The following code works without problems in Python3:
response = self.connection.execute("SELECT EXISTS(SELECT 1 FROM invoices WHERE id=?)", (self.id, ))
fetched = response.fetchone()[0]
if fetched == 1:
print("Exist")
else:
print("Does not exist")
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