同一个MySQL数据库中两个表的某一个字段数据比对

   SELECT a.date_3 - b.date_3 FROM tab1 a,tab2 b WHERE b.numb = a.numb

前提是tab1和tab2都要有对应的numb

如何比较2个mysql数据库数据

sql语句：因为MySQL 没有full outer join,所以用left join union all right join来实现

select a.table_schema,

a.table_name,

a.column_name,

b.table_schema,

b.table_name,

b.column_name

from information_schema.columns a

left join information_schema.columns b on a.table_name = b.table_name and a.column_name =

b.column_name andb.table_schema = 'DBNAMe1'

where a.table_schema = 'DBNAME2' and

(b.table_name is null or

b.column_name is null)

union all

select a.table_schema,

a.table_name,

a.column_name,

b.table_schema,

b.table_name,

b.column_name

from information_schema.columns a

left join information_schema.columns b on a.table_name = b.table_name and a.column_name =

b.column_name andb.table_schema = 'DBNAME2'

where a.table_schema = 'DBNAME1' and

(b.table_name is null or

b.column_name is NULL)

写了一个比较ip地址前半部分的函数，以你给的两个ip为例：

<?php

function ip_part_same($ip1, $ip2) {

$ip1_arr = explode('.', $ip1)

$ip1_f2 = $ip1_arr[0] . $ip1_arr[1]

$ip2_arr = explode('.', $ip2)

$ip2_f2 = $ip2_arr[0] . $ip2_arr[1]

return ($ip1_f2 == $ip2_f2) ? true : false

}

$ip1 = '218.64.81.38'

$ip2 = '183.59.40.203'

if (ip_part_same($ip1, $ip2)) {

echo "ip1和ip2前半部分相同\n"

} else {

echo "ip1和ip2前半部分不同\n"

}

?>

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