php - 列 取决于其他列

Question

我创建了一个名为“members”的 mysql 表，其中 payment 和 ewallet 是两列...我想创建 ewallet 列，以便在付款更新时它会自动更新...规则将是ewallet=0.75* payment。怎么可能？

还有另一列“enroller_id”，我通过它使用 php 函数计算左计数和右计数下线

function getTotalLeg($node,$leg){
$sql="select enrolled_id from members where enroller_id='$node' and tside='$leg' and active='1'";

$res=mysql_query($sql);

global $total;

$total=$total+mysql_num_rows($res);
$row=mysql_fetch_array($res);

 if($row['enrolled_id']!=''){
   getTotalLeg ($row['enrolled_id'],0);
   getTotalLeg ($row['enrolled_id'],1);
  }

return $total;
}

可以在数据库中统计吗？请详细帮助我。提前致谢。

Answer 1

您可以使用generated columns (MySQL 5.7.6+):

Values of a generated column are computed from an expression included in the column definition.

Generated column definitions have this syntax:

col_name data_type [GENERATED ALWAYS] AS (expression) [VIRTUAL | STORED] [UNIQUE [KEY]] [COMMENT comment] [[NOT] NULL] [[PRIMARY] KEY]

CREATE TABLE members(
   ...,
   ewallet DECIMAL(14,4) AS (0.75 * payment)
);