amrishlal commented on pull request #7678:
URL: https://github.com/apache/pinot/pull/7678#issuecomment-962528789
The column names in the resultset look good now, but I think there is more
here than meets the eye. During runtime `AsTransformFunction` is being
constantly called by `DistinctOperator`. This appears to be redundant since
`AsTransformFunction` is simply passing the underlying resultset and has no use
during runtime. I think this can be fixed by making the following modification
to `BrokerRequestToQueryContextConverter.java`:
```
case "DISTINCT":
// Handle alias
operands = thriftExpression.getFunctionCall().getOperands();
for (Expression operand : operands) {
if (operand.isSetFunctionCall() &&
operand.getFunctionCall().getOperator().equalsIgnoreCase("AS")) {
List<Expression> asOperands =
operand.getFunctionCall().getOperands();
aliasList.add(asOperands.get(1).getIdentifier().getName());
// Now that alias has been set, we don't need AS function,
so replace AS function with its first
// operand.
Expression mainOperand = asOperands.get(0);
operand.setType(mainOperand.getType());
operand.unsetFunctionCall();
switch (mainOperand.getType()) {
case LITERAL:
operand.setLiteral(mainOperand.getLiteral());
break;
case FUNCTION:
operand.setFunctionCall(mainOperand.getFunctionCall());
break;
case IDENTIFIER:
operand.setIdentifier(mainOperand.getIdentifier());
break;
}
} else {
aliasList.add(null);
}
}
break;
```
However, this fix still appears a bit "hacky" since AsTransformFunction is
used only during compile time and then discarded. One way to fix this might be
to modify `org.apache.pinot.common.request.Function` to contain a list of
output aliases (?) Since DISTINCT is a Function that outputs an entire row (and
there are probably other functions like this), it makes sense for `Function` to
have a list of aliases for the row output as well (?) and this will avoid the
use of `AsTransformFunction` and all we would need to do is to fetch the list
of aliases from the Function and set it (?)
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