Python, my SQL query return 0 rows

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Hello,

I am using below query and query returns 100 records in MYSQL workbench but returns 0 in python cursor.

import MySQLdb as dbapi
import sys

QUERY="SET @row_number = 0; select * from (SELECT (@row_number:=@row_number + 1) AS '#input', t.* from view t LIMIT 100) as T;"
        db=dbapi.connect(Dbconnection)
        cur=db.cursor()
        cur.execute(QUERY)
        result=cur.fetchall()

In result I get 0 records, may be executing SET @rownumber first might return 0 rows. I don't have permission to create store procedure

What I have tried:

I am trying to add new column in csv with numbering but I believe it will affect performance

Posted 21-May-21 5:00am

RAHUL(10217975)

Updated 21-May-21 7:06am

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CHill60 · Answer 1 · 2021-05-21T07:06:00

Solution 1

You are using the table alias T twice. Try
Python

QUERY="SET @row_number = 0; select * from (SELECT (@row_number:=@row_number + 1) AS '#input', t.* from view t LIMIT 100) as X;"
That was a glitch at my end.

As you have multiple statements in QUERY try

Python

cur.execute(QUERY, multi=True)

Beware: this can have different behaviour depending on which drivers you are using, so it's not the recommended approach.

If you have MySQL V8.0 or better then you could use the ROW_NUMBER [^] function to get the same result

SQL

ROW_NUMBER() OVER () AS rn, ID from view;

Posted 21-May-21 7:06am

CHill60

Updated 22-May-21 4:38am

v3

Comments

RAHUL(10217975) 21-May-21 14:12pm

Query works fine in mysql query editor. But same query returns 0 result in python

CHill60 21-May-21 14:15pm

When I ran it in SQL fiddle I got 0 rows returned. When I changed it to X I got 1 row returned. I had 1 row on my rest table.
Might be a failing of sql fiddle though.
Did you actually try this fix?

RAHUL(10217975) 22-May-21 8:34am

Indeed!
result is 0 records

CHill60 22-May-21 10:26am

Well that started working for me now too - must have been a temporary glitch with the fiddle site. I'm updating my solution with an alternative