Php 使用默认值优化多个表上的查询

我正在尝试使用Recover Cart Sales贡献在一个旧的osCommerce站点上优化一些非常慢的查询

我试图从Cart和customers表中提取信息，我可以很容易地做到这一点。诀窍是我需要弄清楚他们最后一次被联系是什么时候，而不必再做另一个查询。它存在于另一个表中，如果我们以前从未联系过他们，那么表中没有enty，因此它应该为null

这就是我所拥有的，它的工作原理是，它只在scart表中有一个条目时才提取数据

SELECT DISTINCT cb.customers_id, c.customers_firstname, c.customers_lastname, c.customers_email_address, sc.datemodified AS last_contacted
    FROM customers_basket cb, customers c, scart sc
        WHERE c.customers_id = cb.customers_id
            AND cb.customers_id = sc.customers_id 
            AND cb.customers_basket_date_added < 20130916 
            AND cb.customers_basket_date_added > 20130101
        AND cb.customers_id NOT IN(SELECT sc.customers_id  //Excludes people we've contacted in the last month
                                FROM scart sc
                        WHERE sc.datemodified >20130816)
    ORDER BY cb.customers_id DESC

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听起来你需要左键连接？如果存在，它将返回您感兴趣的行；如果不存在，它将返回NULL

SELECT DISTINCT cb.customers_id, c.customers_firstname, c.customers_lastname, c.customers_email_address, sc.datemodified AS last_contacted
FROM customers_basket cb 
INNER JOIN customers c ON c.customers_id = cb.customers_id
LEFT JOIN scart sc ON cb.customers_id = sc.customers_id
WHERE cb.customers_basket_date_added < 20130916 
  AND cb.customers_basket_date_added > 20130101
  AND cb.customers_id NOT IN(SELECT sc.customers_id  //Excludes people we've contacted in the last month
                            FROM scart sc
                    WHERE sc.datemodified >20130816)
ORDER BY cb.customers_id DESC

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完美的我的连接很糟糕！谢谢