Question

我有以下SQL查询，可在MySQL服务器上进行批量更新：

UPDATE res_booking AS rbg
SET rbg.host_id = (
    SELECT vw.entity_id FROM res_booking AS rb
    INNER JOIN pass_single as ps ON (ps.book_id = rb.booking_id)
    INNER JOIN voucher_who as vw ON (vw.pass_id = ps.pass_id)
    WHERE rb.booking_id = rbg.booking_id
)
WHERE rbg.host_id IS NULL;

执行它，给我以下错误：

Error Code: 1093. You can't specify target table 'rbg' for update in FROM clause

该查询如何被重写，因此可以正常工作？

Answer 1

我会将其写为更新联接：

UPDATE res_booking AS rbg
INNER JOIN res_booking AS rb
    ON rb.booking_id = rbg.booking_id
INNER JOIN pass_single AS ps
    ON ps.book_id = rb.booking_id
INNER JOIN voucher_who AS vw
    ON vw.pass_id = ps.pass_id
SET
    rbg.host_id = vw.entity_id
WHERE
    rbg.host_id IS NULL;

从技术上讲，res_booking上的自联接应该是左联接，因为无论子查询是否返回值，您的当前更新都将始终分配给每个记录。但是，我怀疑内部联接逻辑正是您真正想要的。

Answer 2

您可以使用相关子查询。只需将a = [0, 15, 50 , 75] dfs = [df.iloc[a[i]:a[i+1]] for i in range(len(a)-1)]留在子查询之外：

res_booking

如果您在子查询中重新使用正在更新的表，则MySQL会产生错误。但是，它不是必需的。只需修复相关子句以使用UPDATE res_booking rbg SET rbg.host_id = (SELECT vw.entity_id FROM pass_single ps JOIN voucher_who vw ON vw.pass_id = ps.pass_id WHERE ps.book_id = rbg.booking_id ) WHERE rbg.host_id IS NULL;表即可。

请注意，如果子查询返回多个行，这可能会返回错误。这是一件好事。如果发生这种情况，您将需要弄清楚如何处理这种情况。

MySQL：如何基于SELECT查询

2 个答案: