php - 插入语句中的 MySql 表标识符

Question

数据库中有表database_product和database_orders，使用p.rid和o.userid选择它们。如何定义p 和o 来指向database_product 和database_orders？

$query = $wpdb->prepare("
        SELECT p.rid, o.userid
        FROM {$this->dbtable}_orders o
        INNER JOIN {$this->dbtable}_product p ON p.productid = o.productid AND p.status = 'active'
        WHERE o.oid = %d AND o.transaction_id = %s
        LIMIT 1
        ",
        $oid, $tid
    );

Answer 1

查询定义中有一个隐式的“as”关键字。 读取查询如下:

SELECT p.rid, o.userid
FROM {$this->dbtable}_orders as o
INNER JOIN {$this->dbtable}_product as p ON p.productid = o.productid AND p.status =   'active'
WHERE o.oid = %d AND o.transaction_id = %s
LIMIT 1

您可以使用“as”关键字为表格添加别名，帮助您编写更短、更清晰的表格 查询

检查http://dev.mysql.com/doc/refman/5.0/en/join.html了解详情