how to get a single result from a SQLite query in python?

问题

Is there an elegant way of getting a single result from an SQLite SELECT query when using python 2.7?

for example:

conn = sqlite3.connect('db_path.db')
cursor=conn.cursor()
cursor.execute("SELECT MAX(value) FROM table")

for row in cursor:
    for elem in row:
        maxVal = elem

is there a way to avoid those nested fors and get the value directly? I've tried

maxVal = cursor[0][0]

without any success.

回答1:

I think you're looking for Cursor.fetchone() :

cursor.fetchone()[0]

回答2:

Or you could write a wrapper function that, given SQL, returns a scalar result:

def get_scalar_result(conn, sql):
    cursor=conn.cursor()
    cursor.execute(sql)

    return cursor.fetchone()[0]

I apologize for the possibly less than syntactically correct Python above, but I hope you get the idea.

回答3:

If you're not using pysqlite which has the built in cursor.fetchone

cursor.execute("select value from table order by value desc limit 1")

回答4:

select count(*) from ... groupy by ... returns None instead of 0, so fetchone()[0] would lead to an exception.

Therefore

def get_scalar_from_sql(sqlcur, sqlcmd):
    # select count(*) from .... groupy by ... returns None instead of 0
    sqlcur.execute(sqlcmd)
    scalar = 0
    tuple_or_None = sqlcur.fetchone()
    if not tuple_or_None is None:
        (scalar,) = tuple_or_None
    return scalar

回答5:

or you can try : cursor.execute("SELECT * FROM table where name='martin'")

来源：https://stackoverflow.com/questions/7011291/how-to-get-a-single-result-from-a-sqlite-query-in-python

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python

sql

sqlite