OBIEE - ORA-00937 - Not a single-group group function

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You may receive this error and below are some causes.

Odbc driver returned an error (SQLExecDirectW).
  Error Details
Error Codes: OPR4ONWY:U9IM8TAC:OI2DL65P
State: HY000. Code: 2057371920. [NQODBC] [SQL_STATE: HY000] 
[nQSError: 10058] A general error has occurred. 
[nQSError: 17001] Oracle Error code: 937, message: ORA-00937: not a single-group group function at OCI call OCIStmtExecute. 
[nQSError: 17010] SQL statement preparation failed. (HY000)

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Solution

Bad aggregation rule

On one percentage measure was the aggregation rule of answer set to default. By setting it on Average the problem was resolved.

By statement not completely defined

To get the grand total of a column, you may use the by syntax:

avg(MyFact.My Measure by)

In combination with the filter function, this may bring problems then just define the by statement completely by adding the group by columns such as:

avg(MyFact.My Measure by MyDimension.MyAttribute1, MyDimension.MyAttribute2)