Using mysql_num_rows with a select within select query

Question

I have just used a select with a select for the first time. It seems to work and I am getting the desired result when I run it in phpMyAdmin. However, when I then use $variable = mysql_num_rows($queryresult); I get nothing. I guess it is null or something as it won't echo. This is the query:

$resultxl = mysql_query(select * from (Select * from mon_content_lid where mon_date_last!='0000-00-00' ORDER BY lid, mon_date_last desc) as x group by `lid`);
$numx1 = mysql_num_rows($resultxl);
echo $numx1;

No result.

And what have you tried to debug the problem? Have you checked whether that query is valid? Whether MySQL reports errors? — Nico Haase
– Nico Haase, Commented May 20, 2019 at 12:35
Hm, as I say, the query gave the correct result in phpMyAdmin without errors , so I think that it is working. I see from the answer below that I am using a 'cursor'. I think perhaps that is the issue here? Perhaps this doesn't work with mysql_num_rows. I will investigate this. — Donquick
– Donquick, Commented May 21, 2019 at 4:42
Not sure what I have done to get downvoted. As i am new to this, I based my question on these two posts: link & link; both give similar levels of detail similar questions similarly phrased, not much debugging info given. They seem to have been warmly received. — Donquick
– Donquick, Commented May 21, 2019 at 4:50
Two hints about your code: a) please share code without syntax errors - the current code is not well formed, as it won't do anything. Really, nothing, it won't compile. b) Check whether mysql_error provides an error message. Don't rely on whatever phpMyAdmin tells you - check for errors in your code. — Nico Haase
– Nico Haase, Commented May 21, 2019 at 6:15
Does this answer your question? Why shouldn't I use mysql_* functions in PHP? — Dharman
– Dharman ♦, Commented Nov 1, 2019 at 0:41

Martin Schmitz · Accepted Answer · 2019-05-20 12:11:51Z

0

If I see it right (didn't tried it out), you do a SELECT an put the result in a virtual column x, so in my opinion, x should be the only delivered column. This one you group by 'lid'.

select * from (...) as x group by `lid`

So 'lid' is, if it is quoted, a text, not a column-name. Try the query qithout the "group" and dump the cursor, maybe you see some results.

answered May 20, 2019 at 12:11

Martin Schmitz

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1 Comment

Donquick Over a year ago

Thank you - i didn't realise i was creating a cursor: i just copied the select within a select from elsewhere as the result i wanted was similar to the example. I will investigate the cursor.

Baracuda078 · Accepted Answer · 2019-05-20 12:34:44Z

-1

Don't use mysql, use the mysqli functions. If i'm right you can't use the mysql functions in php7 anymore

$db = new mysqli(DB_HOST, DB_USER, DB_PASSWORD, DB_NAME);
$sql = "Here your sql query";
$query_result = mysqli_query($db, $sql);
$number = mysqli_num_rows($query_result);
echo $number;

I didn't test is, but i think this should work. If it still don't work try to see if there are any errors.

die(mysqli_error($db));

edited May 20, 2019 at 12:34

answered May 20, 2019 at 12:29

Baracuda078

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3 Comments

Nico Haase Over a year ago

Don't you think that the result would be completely different if mysql* would not be available?

Donquick Over a year ago

Thanks for answering. No, this is not the issue. I have many instances of mysql which work fine. (We have not updated the site yet).

Baracuda078 Over a year ago

And what if you write the query just like this "select * from mon_content_lid where mon_date_last != '0000-00-00' group by lid order by lid, mon_date_last desc"

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