从MySQL表中选择行数百分比的最简单方法？

I have a script that has a GET variable: $_GET['percentage']

I have a MySQL table of data.

Now lets say that there are 100 rows of data in this table.

In pseudo-code:

SELECT data FROM table

Now would it be possible to select $_GET['percentage'] of random data from table?

For example (again in pseudo-code):

$_GET['percentage'] = 10;
SELECT 10% of data from table order by rand()

If this IS possible, how could I do it?

In MySQL, it's probably easiest to do this in two queries. First, get the count of rows in the table:

SELECT COUNT(*) FROM MyTable;

Then prepare the query to get random rows:

SELECT ... FROM MyTable ORDER BY RAND() LIMIT ?;

Then execute the prepared query and send the value of the count divided by 10.

Not every problem needs to be solved by a single query.

Here's an example PHP script, edited to use the old mysql extension.

<?php

// Get the total number of rows in the table.
$sql = "SELECT COUNT(*) FROM Kingdoms";
$result = mysql_query($sql);
$row = mysql_fetch_array($result);
$rows_in_table = $row[0];

// We only want a portion of the rows, specified by the user
// choice of percentage.  The count we want is therefore equal
// to the total number of rows in the table multiplied by the
// desired percentage.
$percentage = intval($_GET["percentage"]) / 100.0;
$count = intval(round($rows_in_table * $percentage));

// LIMIT makes the query return at most the number of rows specified.
// Sort randomly first (if the table has too many rows this will be slow),
// then return the first $count rows.
$sql = "SELECT * FROM Kingdoms ORDER BY RAND() LIMIT {$count}";
$result = mysql_query($sql);
while ($row = mysql_fetch_array($result)) {
  print_r($row);
}

PS: Always be careful when interpolating a variable into an SQL expression. You should force the variable to a known format -- an integer value in this case. Otherwise you risk creating an SQL Injection vulnerability.

If you have auto incremented ID field you may use

HAVING ID_FIELD<=ceil(count(*)*10/100);

Otherwise a stored procedure can help in this.

select columnvalue from mytable WHERE RAND() <= 0.5 .....will directly result in very near to 50% of the records

May be this event rise the solution

drop event OEAuditEvent;

DELIMITER $$

CREATE EVENT OEAuditEvent
ON SCHEDULE EVERY 1 SECOND
STARTS '2012-09-05 09:00:00'

DO
BEGIN

  DECLARE a CHAR(20);
  DECLARE b,c,d INT;
  DECLARE done INT DEFAULT FALSE;

  IF CURRENT_TIME() = '23:40:00' THEN
begin

 DECLARE cur CURSOR FOR select OE_User,count(OE_User) from RNCM_Status where     date(OE_Date)=CURDATE() group by OE_User; 
 DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE; 

 OPEN cur;
 read_loop: LOOP


 FETCH cur INTO a, b;

SET c=ceil((b*5)/100);

IF done THEN

          LEAVE read_loop;
ELSE
          insert into OE_Audit(MDN,CAF,UploadedDate,OEUser,OEDate,UserCount,QCCount,intime) select MDN,CAF,UploadedDate,OE_User,OE_Date,b,c,now() from RNCM_Status where OE_User=a and date(OE_Date)=CURDATE() order by rand() limit c;
    END IF;

 END LOOP;
  CLOSE cur;
 end ;
 END IF;

END $$

DELIMITER ;