Question

我正在尝试将另一个表添加到已经运行的查询中，但由于某种原因我收到错误。我不确定查询是否足以继续，因为它是由另一个函数运行但我认为它可能只是我的查询..

以下是有效的原始查询：

$listing_sql = "select " . $select_column_list . " p.products_id, p.products_model,   

p.manufacturers_id, p.products_price, p.products_tax_class_id, IF(s.status, 
s.specials_new_products_price, NULL) as specials_new_products_price, IF(s.status, 
s.specials_new_products_price, p.products_price) as final_price 

from " . TABLE_PRODUCTS_DESCRIPTION . " pd, " . TABLE_PRODUCTS . " p 
left join " . TABLE_MANUFACTURERS . " m on p.manufacturers_id = m.manufacturers_id 
left join " . TABLE_SPECIALS . " s on p.products_id = s.products_id,
" . TABLE_PRODUCTS_TO_CATEGORIES . " p2c

where p.products_status = '1' and p.products_id = p2c.products_id and 
pd.products_id = p2c.products_id and pd.language_id = '" . (int)$languages_id . "' and 
p2c.categories_id = '" . (int)$current_category_id . "'";

这是带有添加的表和where子句的新查询（TABLE_PRODUCTS_ATTRIBUTES是新表pa）：

$listing_sql = "select " . $select_column_list . " p.products_id, p.products_model, 
p.manufacturers_id, p.products_price, pa.products_values_id, p.products_tax_class_id, 
IF(s.status, s.specials_new_products_price, NULL) as specials_new_products_price, 
IF(s.status, s.specials_new_products_price, p.products_price) as final_price 

from " . TABLE_PRODUCTS_DESCRIPTION . " pd, " . TABLE_PRODUCTS . " p, " . 

TABLE_PRODUCTS_ATTRIBUTES . " pa
left join " . TABLE_MANUFACTURERS . " m on p.manufacturers_id = m.manufacturers_id 
left join " . TABLE_SPECIALS . " s on p.products_id = s.products_id,
" . TABLE_PRODUCTS_TO_CATEGORIES . " p2c

where p.products_status = '1' and p.products_id = p2c.products_id and p.products_id = 
pa.products_id and pd.products_id = p2c.products_id and pd.language_id = '" . 
(int)$languages_id . "' and p2c.categories_id = '" . (int)$current_category_id . "'";

我的查询是否有任何问题？

Answer 1

问题是您将逗号样式的连接语法与JOIN关键字混合在一起。因为它们具有不同的优先级，所以连接不按预期的顺序执行（您可能期望从左到右的顺序）。

MySQL manual特别警告混合两种类型的连接：

但是，逗号运算符的优先级小于INNER JOIN，CROSS JOIN，LEFT JOIN等。如果在存在连接条件时将逗号连接与其他连接类型混合，则可能会出现'on子句'中未知列'col_name'形式的错误。

您可以修改错误的简单更改是切换TABLE_PRODUCTS_ATTRIBUTES和TABLE_PRODUCTS的顺序：

from " . TABLE_PRODUCTS_DESCRIPTION . " pd, "
. TABLE_PRODUCTS_ATTRIBUTES . " pa, "
. TABLE_PRODUCTS . " p

然而，这并不能解决实际问题 - 您的查询无法维护。更好的是更改所有逗号样式的联接以使用JOIN关键字。这将需要从头开始重写整个查询，但这将使将来更容易修改。

Answer 2

尝试在查询中更改该行：

from " . TABLE_PRODUCTS_DESCRIPTION . " pd, " . TABLE_PRODUCTS . " p, " . TABLE_PRODUCTS_ATTRIBUTES . " pa

致：

from (" . TABLE_PRODUCTS_DESCRIPTION . " pd, " . TABLE_PRODUCTS . " p, " . TABLE_PRODUCTS_ATTRIBUTES . " pa)

括号将不确定表格加入的顺序是您期望的顺序。

我的SQL查询有什么问题？

2 个答案: