mySQL加入哪里？

Question

是否可以将WHERE添加到mysql JOIN语句中，例如：

$result = mysql_query("SELECT * FROM site_products JOIN site_trans ON site_products.product_count = site_trans.trans_inventory WHERE site_products.product_id = site_trans.trans_product");

这可能吗？

Answer 1

是的，这是可能的，但您的查询可能无法提供所需的结果：

SELECT * FROM site_products 
JOIN site_trans ON site_products.product_count = site_trans.trans_inventory 
WHERE site_products.product_id = site_trans.trans_product

相反，您应该将其写为附加的JOIN条件，如此

SELECT * FROM site_products 
JOIN site_trans ON site_trans.trans_inventory = site_products.product_count
     AND site_trans.trans_product = site_products.product_id

您还可以添加WHERE子句

SELECT * FROM site_products 
JOIN site_trans ON site_trans.trans_inventory = site_products.product_count
     AND site_trans.trans_product = site_products.product_id
WHERE site_products.product_id = 2

Answer 2

SELECT * FROM site_products JOIN site_trans ON (site_products.product_count = site_trans.trans_inventory AND site_products.product_id = site_trans.trans_product)
WHERE 1

Answer 3

是的，这可以在MYSQL连接查询中的条件中使用。即使你可以在使用AND运算符的情况下使用多个条件。