PHP＆amp; MySQL：做出化学反应

Question

我有2张桌子 1- tbl_reaction就像这样：

╔════╦═══════════╦════════════╦═════════╗
║ id ║ condition ║ phenomenon ║  infor  ║
╠════╬═══════════╬════════════╬═════════╣
║  1 ║ abcd123   ║ abcd123    ║ abcd123 ║
║  2 ║ wer       ║ wer        ║ wer     ║
╚════╩═══════════╩════════════╩═════════╝

2- tbl_reaction_item喜欢这样：

╔══════╦═══════════╦═════════╦═════╗
║ reid ║ substance ║  type   ║ num ║
╠══════╬═══════════╬═════════╬═════╣
║    1 ║ H2        ║ income  ║   2 ║
║    1 ║ O2        ║ income  ║   1 ║
║    1 ║ H2O       ║ outcome ║   2 ║
╚══════╩═══════════╩═════════╩═════╝

什么是mysql查询来显示反应：

收入+收入=结果

2H2 + O2 =＆gt; 2H2O

Answer 1

  

什么是mysql查询来显示这样的反应:(收入+   收入=＆gt;结果）H2 + O2 =＆gt; H 2 O

SELECT CONCAT(GROUP_CONCAT(CASE WHEN type='income' THEN CONCAT(IF(num=1, '', num),substance) END SEPARATOR ' + '), ' => ',
             GROUP_CONCAT(CASE WHEN type='outcome' THEN CONCAT(IF(num=1, '', num),substance) END SEPARATOR ' + '))
             AS reaction
FROM tbl_reaction_item
GROUP BY reid;

的 SqlFiddleDemo

输出：

╔══════════════════╗
║     reaction     ║
╠══════════════════╣
║ 2H2 + O2 => 2H2O ║
╚══════════════════╝

工作原理：

1. 利用自定义分隔符GROUP_CONCAT ' + '来构建左侧和右侧。
2. 使用CONCAT与=>
加入双方
3. 使用条件聚合分别获得收入/结果
4. 使用1功能删除num IF（也可以使用CASE）

考虑使用GROUP_CONCAT(... ORDER BY pos)添加位置列以始终获得相同的连续字符串部分顺序：

╔══════╦═══════════╦═════════╦═════╦══════╗
║ reid ║ substance ║  type   ║ num ║ pos  ║
╠══════╬═══════════╬═════════╬═════╬══════╣
║    1 ║ H2        ║ income  ║   2 ║   1  ║     -- hydrogen always first
║    1 ║ O2        ║ income  ║   1 ║   2  ║     -- second oxygen
║    1 ║ H2O       ║ outcome ║   2 ║   1  ║
╚══════╩═══════════╩═════════╩═════╩══════╝

附录

您应该更改架构。将主键添加到tbl_reaction_item并使用reid作为外键。

SELECT t1.*, t2.reaction
FROM tbl_reaction t1
LEFT JOIN (
  SELECT reid, CONCAT(GROUP_CONCAT(CASE WHEN type='income' THEN CONCAT(IF(num=1, '', num),substance) END SEPARATOR ' + '), ' => ',
             GROUP_CONCAT(CASE WHEN type='outcome' THEN CONCAT(IF(num=1, '', num),substance) END SEPARATOR ' + '))
             AS reaction
  FROM tbl_reaction_item
  GROUP BY reid
) t2
  ON t1.id = t2.reid

的 SqlFiddleDemo2

输出：

╔═════╦════════════╦═════════════╦══════════╦══════════════════╗
║ id  ║ condition  ║ phenomenon  ║  infor   ║     reaction     ║
╠═════╬════════════╬═════════════╬══════════╬══════════════════╣
║  1  ║ abcd123    ║ abcd123     ║ abcd123  ║ 2H2 + O2 => 2H2O ║
║  2  ║ wer        ║ wer         ║ wer      ║ (null)           ║
╚═════╩════════════╩═════════════╩══════════╩══════════════════╝

Answer 2

我喜欢lad的SQL解决方案，但您也可以使用PHP。请注意，我还没有对它进行测试，并认为添加字符串时出现错误，但您明白了。

$income=[];
$outcome=[];
$stmt=$conn->prepare('SELECT substance,type,num FROM tbl_reaction_item WHERE reid=?');
$stmt->execute(array(1));
while($row=$stmt->fetch()){
    if($row->type=='income') {$income[]=$row->num+$row->substance;}
    else {$outcome[]=$row->num+$row->substance;}
}
echo(implode(' + ',$income).' => '.implode(' + ',$outcome));