检查sqlite3中是否存在行？

Question

How do I properly check if a row exists in my database table using Python 3 and sqlite3?

Here's my original code:

cursor.execute("SELECT name, age FROM people WHERE pin=?", (pin, ))
name, age = cursor.fetchone() or ('', 0)

So currently I'm setting them a default value with the or ('', 0) , and I really don't like this.

Is there a way to check if the person already exists? Something like this (pseudo):

if cursor.exists("pin IN people"):
    cursor.execute("SELECT name, age FROM people WHERE pin=?", (pin, ))
    name, age = cursor.fetchone()

Answer 1

Don't call fetchone() ; just treat the cursor as an iterator:

for row in c.execute("SELECT name, age FROM ..."):
    name, age = row
    break
else:
    print("not found")

Answer 2

Something like this?

vals = cursor.execute("SELECT name, age FROM people WHERE pin=?", (pin, )).fetchone()

if vals:
    name, age = vals

Answer 3

You could use a count query:

if c.execute("SELECT count(*) FROM people WHERE pin=?", (pin, )).fetchone()[0] > 0:
    ...

Answer 4

Alternatively you may use EXISTS to validate the query if your table is large and you will benefit with index on pin , take a look at this SO , so you may do:

c = cursor.execute("""SELECT EXISTS (SELECT 1 
                                     FROM people 
                                     WHERE pin=?
                                     LIMIT 1)""", (pin, )).fetchone()[0]
if c:
    ...

The cursor will return either (1,) (if 1 or more rows returned) or (0,) (if None returned), c will be either 1/0 as fetchone()[0] will get the integer value 1/0 from above.

Exists could be more efficient depending on the size of your table and if you have index set on the field you query.