mysql>
select
SQRT(16)
+----------+
|
SQRT(16)
|
+----------+
|
4.000000
|
+----------+
1
row
in
set
(0.00
sec)
所看到的浮点值,因为内部MySQL将处理浮点数据类型的平方根。
可以使用SQRT函数,计算出记录的平方根。了解SQRT函数更详细用法,考虑EMPLOYEE_TBL的表具有以下记录:
mysql>
SELECT
*
FROM
employee_tbl
+------+------+------------+--------------------+
|
id
|
name
|
work_date
|
daily_typing_pages
|
+------+------+------------+--------------------+
|
1
|
John
|
2007-01-24
|
250
|
|
2
|
Ram
|
2007-05-27
|
220
|
|
3
|
Jack
|
2007-05-06
|
170
|
|
3
|
Jack
|
2007-04-06
|
100
|
|
4
|
Jill
|
2007-04-06
|
220
|
|
5
|
Zara
|
2007-06-06
|
300
|
|
5
|
Zara
|
2007-02-06
|
350
|
+------+------+------------+--------------------+
7
rows
in
set
(0.00
sec)
假设根据上面的表格,要计算所有的dialy_typing_pages的平方根,然后可以通过使用下面的命令:
mysql>
SELECT
name,
SQRT(daily_typing_pages)
->
FROM
employee_tbl
+------+--------------------------+
|
name
|
SQRT(daily_typing_pages)
|
+------+--------------------------+
|
John
|
15.811388
|
|
Ram
|
14.832397
|
|
Jack
|
13.038405
|
|
Jack
|
10.000000
|
|
Jill
|
14.832397
|
|
Zara
|
17.320508
|
|
Zara
|
18.708287
|
+------+--------------------------+
7
rows
in
set
(0.00
sec)
<?phpheader("Content-type:text/htmlcharset=utf-8")
$count = 0//该变量用来统计素数个数,并初始化为0
echo "素数:"
for($i=2$i<34$i++)
{
for($j=2$j<=intval(sqrt($i))$j++)
{
if($i%$j==0)
{
$isPrime=false
break
}
$isPrime=true
}
if($isPrime)
{
$count = $count + 1//是素数,所以统计变量加1
echo $i ." "
}
}
echo "素数的个数为:".$count
?>
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