Postgresql Join on Select 语句
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Postgresql Join on Select Statement
提问by Stanley Cup Phil
I want to do a join on a SelectStatement in Postgresql, but I am having issues
我想加入SelectPostgresql 中的语句，但我遇到了问题
SELECT
s.sessionid, sp.lang
FROM
sessions s
INNER JOIN
pages sp
ON
sp.sessionid = s.sessionid
INNER JOIN
(
SELECT
max(sessionid)
FROM
sessions
AS
maxSession
)
ON
maxSession = s.sessionid
WHERE
--Where condition
I get the following error: ERROR: subquery in FROM must have an alias
我收到以下错误：错误：FROM 中的子查询必须有一个别名
LINE 6: (
^
HINT: For example, FROM (SELECT ...) [AS] foo.
If I add the FROM
如果我添加 FROM
FROM
(
SELECT max(sessionid)
FROM sessions
)
AS maxSession
I get another error
我收到另一个错误
ERROR: syntax error at or near "FROM"
LINE 7: FROM
Ideas?
想法？
回答by Twelfth
You are close.
你很近。
INNER JOIN
(
SELECT
max(sessionid) as 'maxSession'
FROM
sessions
) maxSession
ON
maxSession.maxSession = s.sessionid
Any time you refer to a query as a table, you need to give it an alias...alias goes right after the entire subquery, not in the subquery itself.
任何时候将查询称为表时，都需要给它一个别名...别名紧跟在整个子查询之后，而不是在子查询本身中。
