how to combine left joins?
In MS Access 2007 query, how can I combine the following 2 queries?
SELECT Tests.Release, Test开发者_C百科cases.TestCase, Tests.Result
FROM Tests LEFT JOIN Testcases ON Tests.TestCaseID=Testcases.ID;
SELECT Tests.Release, ResultEnums.Result
FROM Tests LEFT JOIN ResultEnums ON ResultEnums.ID=Tests.Result;
Thanks
Access has this craptastic "feature" which requires you pair your joins in parentheses:
Select Tests.Release, Testcases.TestCase, Tests.Result, ResultEnums.Result
From (Tests
Left Join TestCases
On TestCases.TestCaseID = Tests.TestCaseID)
Left Join ResultEnums
On ResultEnums.ID = Tests.Result
This type of query can produce some bad results depending on the schema. If for a given Tests row, multiple TestCases rows and multiple ResultEnums rows are returned, those rows will be combined via a cross product with each other. For example, if a given Tests row returned five TestCases rows and three ResultEnums rows, you will get 15 rows for that Tests row. However, if say ResultEnums is parent to the Tests table (thus for every Tests row, you would only get one ResultEnums value), then this should work fine.
I can't test now but you surely need parenthesis:
SELECT Tests.Release
, Testcases.TestCase
, Tests.Result
, ResultEnums.Result
FROM ( Tests
LEFT JOIN Testcases
ON Tests.TestCaseID=Testcases.ID
)
LEFT JOIN ResultEnums
ON ResultEnums.ID=Tests.Result
;
or
SELECT Tests.Release
, Testcases.TestCase
, Tests.Result
, ResultEnums.Result
FROM ( Tests
LEFT JOIN ResultEnums
ON ResultEnums.ID=Tests.Result
)
LEFT JOIN Testcases
ON Tests.TestCaseID=Testcases.ID
;
A very naive/simplified solution would be to simply UNION ALL them:
SELECT Tests.Release, Testcases.TestCase, Tests.Result
FROM Tests LEFT JOIN Testcases ON Tests.TestCaseID=Testcases.ID;
UNION ALL
SELECT Tests.Release, NULL, ResultEnums.Result
FROM Tests LEFT JOIN ResultEnums ON ResultEnums.ID=Tests.Result;
edit: update for comment here
I think this is what you want, the Result from the ResultEnums table, the Release from the Tests table, and the associated TestCase from the Testcases table, all JOINed on their keys:
SELECT
re.Result
,t.Release
,tc.TestCase
FROM
Tests t
LEFT JOIN TestCases tc ON t.TestCaseID = tc.ID
LEFT JOIN ResultEnums re ON re.ID = t.Result
SELECT Tests.Release, Testcases.TestCase, Tests.Result, ResultEnums.Result
FROM Tests LEFT JOIN Testcases ON Tests.TestCaseID=Testcases.ID
LEFT JOIN ResultEnums ON ResultEnums.ID=Tests.Result;
EDIT I didn't test on Access, but in SQL Server you could do something akin to this.
加载中,请稍侯......
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