为什么'；MySQL是否在JOIN plus ORDER上使用主键？

这里有一个简单的例子（显然是MySQL）：

上面的查询（同样，这正是我在生产中运行的查询）运行大约需要14秒。下面是在生产环境中执行的简化查询，如上面的用例所示：

SELECT corder.id, invoice.invoice_no FROM corder LEFT JOIN invoice ON invoice.id=corder.invoice ORDER BY corder.id DESC LIMIT 400, 20; 此操作失败，并显示以下错误消息：

ERROR 1235 (42000): This version of MySQL doesn't yet support 'LIMIT & IN/ALL/ANY/SOME subquery' 错误1235（42000）：此版本的MySQL尚不支持“LIMIT&IN/ALL/ANY/SOME子查询” 我使用的是MySQL 5.1.61，它在5.1系列中是相当新的（显然这在5.5.x中也不受支持）。

您能试试这个版本吗（它基本上先获取

corder

表的420行，保留其中的20行，然后进行3个外部联接）：

---

您在加入中使用的

客户订单（发票）

上没有索引吗？我的意思是，在生产系统中。使用5行表进行测试没有什么价值。执行计划可能不同于实际计划（有很多行）。实际上，在我试图理解这一点时，我尝试添加了它，但没有任何区别（如果你仔细想想，这是意料之中的）。是的，我是在生产中这样做的——没有区别。第二，表是MyISAM还是InnoDB？这是有区别的。最后，你的最后一个（有问题的）查询是相当无用的。您（左）加入到

customer\u invoice

，但在选择时不使用它。如果你发布一个有用的查询，那就更好了。否则，为什么要使用第四行，这只是第二行（但可能有很多重复行）？MyISAM。如果您愿意，您可以在该查询中添加铃铛和哨子，这不会有任何区别（我显然选择的不仅仅是订单ID）。0.09秒，而之前为12-14秒。这是我之前说过的好办法。敬你一杯，先生！我很难过，似乎没有办法强迫MySQL自己做这件事，但我想这是最好的了。 +----+-------------+-------+--------+---------------+---------+---------+-----------------------------+------+-------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+--------+---------------+---------+---------+-----------------------------+------+-------------+ | 1 | SIMPLE | co | ALL | NULL | NULL | NULL | NULL | 5 | | | 1 | SIMPLE | ci | eq_ref | PRIMARY | PRIMARY | 3 | index_test_gutza.co.invoice | 1 | Using index | +----+-------------+-------+--------+---------------+---------+---------+-----------------------------+------+-------------+ +----+-------------+-------+--------+---------------+---------+---------+-----------------------------+------+----------------+ | id | select_type | table | type | possible_keys | key | key_len | ref | rows | Extra | +----+-------------+-------+--------+---------------+---------+---------+-----------------------------+------+----------------+ | 1 | SIMPLE | co | ALL | NULL | NULL | NULL | NULL | 5 | Using filesort | | 1 | SIMPLE | ci | eq_ref | PRIMARY | PRIMARY | 3 | index_test_gutza.co.invoice | 1 | Using index | +----+-------------+-------+--------+---------------+---------+---------+-----------------------------+------+----------------+ SELECT corder.id, corder.public_id, CONCAT(buyer.fname," ",buyer.lname) AS buyer_name, corder.status, corder.payment, corder.reserved AS R, corder.tracking_id!="" as A, corder.payment_received as pay_date, invoice.invoice_no AS inv, invoice.receipt_no AS rec, invoice.public AS pub_inv, proforma.proforma_no AS prof, proforma.public AS pub_pf, corder.rating, corder.rating_comments!="" AS got_comment FROM corder LEFT JOIN user as buyer ON buyer.id=corder.buyer LEFT JOIN invoice as invoice ON invoice.id=corder.invoice LEFT JOIN invoice as proforma ON proforma.id=corder.proforma ORDER BY id DESC LIMIT 400, 20; SELECT corder.id, invoice.invoice_no FROM corder LEFT JOIN invoice ON invoice.id=corder.invoice ORDER BY corder.id DESC LIMIT 400, 20; SELECT corder.id, corder.public_id, CONCAT(buyer.fname," ",buyer.lname) AS buyer_name, corder.status, corder.payment, corder.reserved AS R, corder.tracking_id != "" AS A, corder.payment_received AS pay_date, invoice.invoice_no AS inv, invoice.receipt_no AS rec, invoice.public AS pub_inv, proforma.proforma_no AS prof, proforma.public AS pub_pf, corder.rating, corder.rating_comments!="" AS got_comment FROM corder LEFT JOIN user as buyer ON buyer.id = corder.buyer LEFT JOIN invoice AS invoice ON invoice.id = corder.invoice LEFT JOIN invoice AS proforma ON proforma.id = corder.proforma WHERE corder.id IN ( SELECT id FROM corder ORDER BY id DESC LIMIT 400,20 ) ORDER BY corder.id DESC; ERROR 1235 (42000): This version of MySQL doesn't yet support 'LIMIT & IN/ALL/ANY/SOME subquery'

SELECT
    corder.id,
    corder.public_id,
    CONCAT(buyer.fname," ",buyer.lname) AS buyer_name,
    corder.status,
    corder.payment,
    corder.reserved AS R,
    corder.tracking_id != "" AS A,
    corder.payment_received AS pay_date,
    invoice.invoice_no AS inv,
    invoice.receipt_no AS rec,
    invoice.public AS pub_inv,
    proforma.proforma_no AS prof,
    proforma.public AS pub_pf,
    corder.rating,
    corder.rating_comments!="" AS got_comment
FROM
    ( SELECT * 
      FROM corder
      ORDER BY
        id DESC 
      LIMIT 400, 20
    )
    AS corder
LEFT JOIN user as buyer ON buyer.id = corder.buyer
LEFT JOIN invoice AS invoice ON invoice.id = corder.invoice
LEFT JOIN invoice AS proforma ON proforma.id = corder.proforma
ORDER BY
    corder.id DESC ;