问题
The example below stops at the first JOIN with an error message
Encountered " "JOIN" "JOIN "" at line 13, column 4. Was expecting: ")"
Am I missing something obvious with multiple joins in Bigquery?
SELECT type.CourseType AS CourseType,
SUM(joined.assign.StudentCount) AS StudentN
FROM
(
SELECT assign.StateCourseCode,
assign.StateCourseName,
assign.MatchType,
assign.Term,
assign.StudentCount
FROM [Assignment.AssignmentExtract5] AS assign
JOIN SELECT wgt.Term,
wgt.Weight
FROM [Crosswalk.TermWeights] AS wgt
ON wgt.Term = assign.Term
) AS joined
JOIN SELECT type.CourseCode,
type.CourseDescription,
type.CourseType,
type.CourseCategory
FROM [Crosswalk.CourseTypeDescription] AS type
ON joined.assign.StateCourseCode = type.CourseCode
GROUP BY CourseType
回答1:
I think you're just missing a parenthesis on line 13.
This:
JOIN SELECT wgt.Term,
wgt.Weight
FROM [Crosswalk.TermWeights] AS wgt
ON wgt.Term = assign.Term
Should be:
JOIN (SELECT wgt.Term,
wgt.Weight
FROM [Crosswalk.TermWeights]) AS wgt
ON wgt.Term = assign.Term
More info: https://developers.google.com/bigquery/docs/query-reference#multiplejoinsexample
FYI - JOINs are not as fast as we'd like yet. We're working on improving the performance.
回答2:
Thanks Ryan, your help was much appreciated. For anyone who might be interested, here is a query that worked.
SELECT type.CourseCategory AS CourseCategory,
SUM(joined.assign.StudentCount) AS StudentN
FROM
(
SELECT assign.StateCourseCode,
assign.StateCourseName,
assign.MatchType,
assign.Term,
assign.StudentCount
FROM [Assignment.AssignmentExtract5] AS assign
JOIN (SELECT Term,
Weight
FROM [Crosswalk.TermWeights]) AS wgt
ON wgt.Term = assign.Term
) AS joined
JOIN (SELECT CourseCode,
CourseDescription,
CourseType,
CourseCategory
FROM [Crosswalk.CourseTypeDescription]) AS type
ON (joined.assign.StateCourseCode = type.CourseCode)
GROUP BY CourseCategory;
来源：https://stackoverflow.com/questions/12333401/joining-3-tables-in-google-bigquery