Question

好的，所以我有一张这样的表

Col1      Col2

10        30
20        40
50        60

我正在查询数据

Query = ("SELECT * FROM TableName");

while ( $row= Mysql_fetch_array($query)) {

  // code will go here 
 Code needs to get the prev row and the current row for every row in the table like:

 This row['col1'] - prev row['col1'] = $wahatever

  echo $whatever



}

我不知道如何引用php中的prev行，因为它通过while语句查看我需要说col1 - prev col1和col2 - prev col2

Anyonw能告诉我怎么做。它实际上用于解决我能做的复杂映射干扰，只是无法解决如何在循环中调用prev行数据。

任何帮助都会受到极大的欢迎

感谢你的帮助，但我不认为我正确地回答了这个问题。

我正在寻找的方法是获取每一行，然后从prev行上的col1减去col1并通过一个循环直到结束。

Answer 1

您可以在SQL解决方案中完整地尝试这个

SELECT col1, col2, 
       col1 - @prev1, 
       col2 - @prev2,
       @prev1 := col1, @prev2 := col2
FROM TableName, (select @prev1 := 0, @prev2 := 0) r

SQLFiddle demo

Answer 2

 $prevRow = null;
 while ( $row= Mysql_fetch_array($query)) {
      if($prevRow != null){
           //comparison here
      }
      $prevRow = $row;
 }

Answer 3

或者，您可以将值首先存储在数组中，如

$myArr = array(); $i=0;
while ( $row= Mysql_fetch_array($query)) {

  // code will go here 
   $myArr[$i] = $row['col1']; 
   $myArr[$i] = $row['col2'];

   $i++;
}

然后你会知道$i-1是db的前一行。

foreach($myArr as $i => $row) {
   if( isset($myArr[$i-1]) {
       $prevRow = $row;
   }
   // blah blah blah
}

Answer 4

您可以使用mysql_data_seek 更改指向当前行的指针然后获取它，但我建议在每个步骤中存储以前的值

Answer 5

如果您要比较2个不同的行，那么如果它们具有主要和自动递增的ID，它们将不会相等，但如果您只是比较行中的特定数据，那么最好的方法是存储它们，或者您可以查询所有行列但不包括id

查询当前查询的id-1，只需确保将id作为主要和自动递增，例如

<?php
$que = "SELECT * FROM table ...'";
res = mysql_query($que, $con);
if(mysql_num_rows($res)>0){
while($row = mysql_fetch_array($res)){ 
$counter=1;//apply this so it will not compare the first row in the data to the previous 
//one because there is nothing to compare
if($counter > 1){//determine if it is the 2nd row therfore do the comparison
$currentrow=$row['id']; //this is the id of the current row which is row 2
$previousrowid=$row['id']-1; //this is the id of the row 1 which you will need to query 
//the datas on it to compare it 

 $que2 = mysql_query("SELECT value FROM table where id= '$previousrowid' ");//query of the previous row
 $r  = mysql_fetch_array($que2);
 $previousdata=$r['data'];
 $currentdata=$row['data'];
 $counter++;
 if($previousdata != $currentdata)
 {
 echo "They Are Not Equal";
 }else{
 echo "They Are Equal!";
 }
 }//ending of the counter


}}//ending of loop
?>

希望这有帮助

用php获取mysql结果中的prev行

5 个答案:

SQLFiddle demo