Re^3: Perl and MySQL: Get number of rows affected

In MySql documentation, I got the below query:

Query from documentation :

SELECT COUNT(ip), AVG(down) from test;
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When I run the below query, i am getting the following output.

Query which I ran:

mysql> select count(us_name) from table where us_name='samy';
+----------------+
| count(us_name) |
+----------------+
|              6 |
+----------------+
1 row in set (0.00 sec)
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Regards,
Velusamy R.

eval"print uc\"\\c$_\""for split'','j)@,/6%@0%2,`e@3!-9v2)/@|6%,53!-9@2~j';

Comment on Re^3: Perl and MySQL: Get number of rows affected Select or Download Code

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Re^4: Perl and MySQL: Get number of rows affected by Ieronim (Friar) on Jul 15, 2006 at 13:23 UTC
It seems that you don't know what the NULL values are :) Yes, in the case when the column `value` is declared as NOT NULL, `COUNT(value)` is equivalent to `COUNT()`. But look at the example: `CREATE TEMPORARY TABLE testnull0 ( id INT NOT NULL auto_increment, value VARCHAR(100), PRIMARY KEY(id) ) ENGINE=MyISAM; INSERT INTO testnull0 (id, value) VALUES (1, 'hello'), (2, 'googbye'), + (3, NULL); SELECT COUNT(id), COUNT(value), COUNT() FROM testnull0;` [download] Being processed by MySQL (you must specify your DB name, of course), it prints: `+-----------+--------------+----------+ \| COUNT(id) \| COUNT(value) \| COUNT() \| +-----------+--------------+----------+ \| 3 \| 2 \| 3 \| +-----------+--------------+----------+` [download] Got the idea? You cannot rely on the suggestion that the `value` column is declared as NOT NULL, if you did not create the table yorself :) while `COUNT()` always works as expected. It's REALLY off-topic here, but i think that answering an OT question wrong is worse than answering it right—and even worse than not answering it at all.	[reply] [d/l] [select]

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Re^4: Perl and MySQL: Get number of rows affected
by Ieronim (Friar) on Jul 15, 2006 at 13:23 UTC

NULL

value

COUNT(value)

COUNT(*)

But look at the example:

CREATE TEMPORARY TABLE testnull0 (
  id INT NOT NULL auto_increment,
  value VARCHAR(100),
  PRIMARY KEY(id)
)
ENGINE=MyISAM;

INSERT INTO testnull0 (id, value) VALUES (1, 'hello'), (2, 'googbye'),
+ (3, NULL);

SELECT COUNT(id), COUNT(value), COUNT(*) FROM testnull0;
[download]

+-----------+--------------+----------+
| COUNT(id) | COUNT(value) | COUNT(*) |
+-----------+--------------+----------+
|         3 |            2 |        3 |
+-----------+--------------+----------+
[download]

value

COUNT(*)

It's REALLY off-topic here, but i think that answering an OT question wrong is worse than answering it right—and even worse than not answering it at all.

[reply]
[d/l]
[select]