本文介绍了MySQL JOIN 与 LEFT JOIN 的区别的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我有这个跨数据库查询...
I have this cross-database query...
SELECT
`DM_Server`.`Jobs`.*,
`DM_Server`.servers.Description AS server,
digital_inventory.params,
products.products_id,
products.products_pdfupload,
customers.customers_firstname,
customers.customers_lastname
FROM `DM_Server`.`Jobs`
INNER JOIN `DM_Server`.servers ON servers.ServerID = Jobs.Jobs_ServerID
JOIN `cpod_live`.`digital_inventory` ON digital_inventory.jobname = Jobs.Jobs_Name
JOIN `cpod_live`.`products` ON products.products_pdfupload = CONCAT(digital_inventory.jobname, ".pdf")
JOIN `cpod_live`.`customers` ON customers.customers_id = products.cID
ORDER BY `DM_Server`.`Jobs`.Jobs_StartTime DESC LIMIT 50
它运行良好，直到我使它们 LEFT JOIN s.我认为通过不指定连接类型，它被假定为 LEFT JOIN.不是这样吗?
it runs fine until I make them LEFT JOINs. I thought that by not specifying a type of join it was assumed to be a LEFT JOIN. Is this not the case?
推荐答案
我认为通过不指定连接类型，它被假定为左连接.不是这样吗?
I thought that by not specifying a type of join it was assumed to be a LEFT JOIN. Is this not the case?
不，默认联接是内部联接.
No, the default join is an INNER JOIN.
这是对SQL 连接.
内连接
左连接
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