Get psycopg2 count(*) number of results

Question

Whats the correct way to get the number or rows returned by this query? I’m specifically looking to see if no results are returned.

sql = 'SELECT count(*) from table WHERE guid = %s;'
data=[guid]
cur.execute(sql,data)
results = cur.fetchone()
for r in results:
  print type(r) # Returns as string {'count': 0L} Or {'count': 1L}

Thanks.

Asked By: Matt

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Source

Answer 1

results is itself a row object, in your case (judging by the claimed print output), a dictionary (you probably configured a dict-like cursor subclass); simply access the count key:

result = cur.fetchone()
print result['count']

Because you used .fetchone() only one row is returned, not a list of rows.

If you are not using a dict(-like) row cursor, rows are tuples and the count value is the first value:

result = cur.fetchone()
print result[0]

Answered By: Martijn Pieters

Answer 2

The following worked for me

cur.execute('select * from table where guid = %s;',[guid])
rows = cur.fetchall()
print 'ResultCount = %d' % len(rows)

Drawback:
This will not be very efficient for the DBMS if all you need is the count.

Answered By: alejandro

Answer 3

This may be helpful to those coming across this thread, here is a way to count all the rows for each table in your database using Python:

total_count = 0

with con.cursor() as cur:
    cur.execute("""SELECT table_name FROM information_schema.tables
           WHERE table_schema = 'public'""")

    for table in cur.fetchall():
        table_name = table[0]
        cur.execute(sql.SQL("SELECT COUNT(*) FROM {table}").format(table=sql.Identifier(table_name)))
        table_count = cur.fetchone()
        result = f'TABLE NAME: {table_name}, COUNT: {table_count}'
        total_count += int(table_count[0])
        print(result)

print(total_count)

Answered By: idcabnun

Get psycopg2 count(*) number of results

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