[python] Python, how to check if a result set is empty?

I have a sql statement that returns no hits. For example, 'select * from TAB where 1 = 2'.

I want to check how many rows are returned,

cursor.execute(query_sql)

rs = cursor.fetchall()

Here I get already exception: "(0, 'No result set')"

How can I prevend this exception, check whether the result set is empty?

Notice: This is for MySQLdb module in Python.

For a SELECT statement, there shouldn't be an exception for an empty recordset. Just an empty list ([]) for cursor.fetchall() and None for cursor.fetchone().

For any other statement, e.g. INSERT or UPDATE, that doesn't return a recordset, you can neither call fetchall() nor fetchone() on the cursor. Otherwise, an exception will be raised.

There's one way to distinguish between the above two types of cursors:

def yield_data(cursor):
    while True:
        if cursor.description is None:
            # No recordset for INSERT, UPDATE, CREATE, etc
            pass
        else:
            # Recordset for SELECT, yield data
            yield cursor.fetchall()
            # Or yield column names with
            # yield [col[0] for col in cursor.description]

        # Go to the next recordset
        if not cursor.nextset():
            # End of recordsets
            return

MySQLdb will not raise an exception if the result set is empty. Additionally cursor.execute() function will return a long value which is number of rows in the fetched result set. So if you want to check for empty results, your code can be re-written as

rows_count = cursor.execute(query_sql)
if rows_count > 0:
     rs = cursor.fetchall()
else:
     // handle empty result set

I had a similar problem when I needed to make multiple sql queries. The problem was that some queries did not return the result and I wanted to print that result. And there was a mistake. As already written, there are several solutions.

if cursor.description is None:
    # No recordset for INSERT, UPDATE, CREATE, etc
    pass
else:
    # Recordset for SELECT

As well as:

exist = cursor.fetchone()
if exist is None:
  ... # does not exist
else:
  ... # exists

One of the solutions is:

The try and except block lets you handle the error/exceptions. The finally block lets you execute code, regardless of the result of the try and except blocks. So the presented problem can be solved by using it.

s = """ set current query acceleration = enable;
        set current GET_ACCEL_ARCHIVE = yes;
        SELECT * FROM TABLE_NAME;"""

query_sqls = [i.strip() + ";" for i in filter(None, s.split(';'))]
for sql in query_sqls:
    print(f"Executing SQL statements ====> {sql} <=====")
    cursor.execute(sql)
    print(f"SQL ====> {sql} <===== was executed successfully")
    try:
        print("\n****************** RESULT ***********************")
        for result in cursor.fetchall():
            print(result)
        print("****************** END RESULT ***********************\n")
    except Exception as e:
        print(f"SQL: ====> {sql} <==== doesn't have output!\n")
        # print(str(e))

output:

Executing SQL statements ====> set current query acceleration = enable; <=====
SQL: ====> set current query acceleration = enable; <==== doesn't have output!

Executing SQL statements ====> set current GET_ACCEL_ARCHIVE = yes; <=====
SQL: ====> set current GET_ACCEL_ARCHIVE = yes; <==== doesn't have output!

Executing SQL statements ====> SELECT * FROM TABLE_NAME; <=====

****************** RESULT ***********************

       ----------   DATA   ----------

****************** END RESULT ***********************

The example above only presents a simple use as an idea that could help with your solution. Of course, you should also pay attention to other errors, such as the correctness of the query, etc.

You can do like this :

count = 0
cnxn = pyodbc.connect("Driver={SQL Server Native Client 11.0};"
                      "Server=serverName;"
                      "Trusted_Connection=yes;")
cursor = cnxn.cursor()
cursor.execute(SQL query)
for row in cursor:
    count = 1
    if true condition:
        print("True")
    else:
        print("False")
if count == 0:
    print("No Result")

Thanks :)

if you're connecting to a postgres database, the following works:

result = cursor.execute(query)

if result.returns_rows:
    # we got rows!
    return [{k:v for k,v in zip(result.keys(), r)} for r in result.rows]
else:
    return None

For reference, cursor.rowcount will only return on CREATE, UPDATE and DELETE statements:

 |  rowcount
 |      This read-only attribute specifies the number of rows the last DML statement
 |      (INSERT, UPDATE, DELETE) affected.  This is set to -1 for SELECT statements.

I had issues with rowcount always returning -1 no matter what solution I tried.

I found the following a good replacement to check for a null result.

c.execute("SELECT * FROM users WHERE id=?", (id_num,))
row = c.fetchone()
if row == None:
   print("There are no results for this query")