[英]How to use subselection result as temp table in MySQL update query?
table A
uid
uname
temp table B
uid
uname
table B is not a real table but a result of subquery like 表B不是真正的表,而是子查询的结果,例如
select uid, uname
from tableC left join tableD on tableC.pid = tableD.pid
where tableC.qid = tableD.qid
group by uid;
I want to update set A.uname = B.uname where A.uid = B.uid 我想更新集合A.uname = B.uname,其中A.uid = B.uid
how can I do that with MySQL? 我该如何使用MySQL?
Treat the subquery as a table in a JOIN
: 将子查询视为
JOIN
的表:
UPDATE tableA AS a
JOIN (select uid, uname
from tableC
left join tableD on tableC.pid = tableD.pid and tableC.qid = tableD.qid
group by uid) AS b ON a.uid = b.uid
SET a.uname = b.uname
Also, note that in a LEFT JOIN
, all the conditions that refer to the second table should be in the ON
clause. 另外,请注意,在
LEFT JOIN
,引用第二个表的所有条件都应在ON
子句中。 Otherwise, you'll filter out all the non-matching rows, because the values of those columns will be NULL
, and that will negate the point of using LEFT JOIN
rather than INNER JOIN
. 否则,您将过滤掉所有不匹配的行,因为这些列的值将为
NULL
,这将否定使用LEFT JOIN
而不是INNER JOIN
。
update a
set uname = B.name
from A a
inner join (
select uname [name]
from tableC left join tableD on tableC.pid = tableD.pid
where tableC.qid = tableD.qid
group by uid ) b
ON a.uid = b.uid
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