mysql - 包含多个 SELECT 的 SQL 语句中的一列返回空值

Question

我从以前的开发人员那里继承了一个特定的代码。我打算重新构建应用程序，但在继续之前我必须添加一些功能。

首先，这是一个与会计有关的 62 列表，我还必须通过一次调用从不同的表中获取值，以便在插入之前获取我需要的值。

假设我需要插入表 dailysales 并且我需要从表 a,b,c 和 d 中获取值同时。 我已经有一个用于获取此值的 sql 语句，它工作正常，只是特定列一直返回为 NULL。 这是我的代码:

SELECT `gds_pnr_ref`, `transaction_date`,
       (SELECT `lastname` FROM `a` WHERE `id` = `staff` LIMIT 1) as `lastname`,
       (SELECT `firstname` FROM `a` WHERE `id` = `staff` LIMIT 1) as `firstname`,
       (SELECT `department_name` FROM `b` WHERE `id` = `staff_department` LIMIT 1) as `department`,
       (SELECT `name` FROM `b` WHERE `memo_serial` = '$some_value' LIMIT 1) as `pax_name`,
       (SELECT `customer_name` FROM `c` WHERE `id` = `customer_name` LIMIT 1) as `customer`,
       travel_product,
       (SELECT `vendor_name` FROM `c` WHERE `id` = `vendor` LIMIT 1) as `vendor` 
FROM `d` WHERE `id` = '$some_value' LIMIT 1

列 (SELECT customer_name FROM c WHERE id = customer_name LIMIT 1) as customer 始终返回为 NULL 但是当我独立运行它时，它会给我适当的值。

我非常愿意接受更好的解决方案来解决这个问题。

Answer 1

您应该始终限定查询中的列名。据推测，您打算这样:

SELECT d.`gds_pnr_ref`, d.`transaction_date`,
       (SELECT a.`lastname` FROM `a` WHERE a.`id` = d.`staff` LIMIT 1) as `lastname`,
       (SELECT a.`firstname` FROM `a` WHERE a.`id` = d.`staff` LIMIT 1) as `firstname`,
       (SELECT b.`department_name` FROM `b` WHERE b.`id` = d.`staff_department` LIMIT 1) as `department`,
       (SELECT b.`name` FROM `b` WHERE b.`memo_serial` = ? LIMIT 1) as `pax_name`,
       (SELECT c.`customer_name` FROM `c` WHERE c.`id` = d.`customer_name` LIMIT 1) as `customer`,
       d.travel_product,
       (SELECT c.`vendor_name` FROM `c` WHERE c.`id` = d.`vendor` LIMIT 1) as `vendor` 
FROM `d`
WHERE d.`id` = ?
LIMIT 1;

我必须猜测列的来源——所以这可能不是 100% 正确。

请注意，我还用 ? 占位符替换了字符串变量。这是一个提醒，您应该为此类值使用参数。