Hi,
Recently, I'm working on the "IOTDB-456: Support Fill function in Group By Fill", the JIRA link is https://issues.apache.org/jira/browse/IOTDB-456. I think we need a new GroupByFillClause to support it. The new GroupByFillClause grammar is shown as the following: SELECT <SelectClause> FROM <FromClause> WHERE <WhereClause> GROUP BY <GroupByClause> (FILL <GROUPBYFillClause>)? GroupByClause : LPAREN <TimeInterval> COMMA <TimeUnit> RPAREN GROUPBYFillClause : LPAREN <TypeClause> RPAREN TypeClause : <AllClause> | <Int32Clause> | <Int64Clause> | <FloatClause> | <DoubleClause> | <BoolClause> | <TextClause> AllClause: ALL LBRACKET (<PreviousUntilLastClause> | <PreviousClause>) RBRACKET Int32Clause: INT32 LBRACKET (<PreviousUntilLastClause> | <PreviousClause>) RBRACKET Int64Clause: INT64 LBRACKET (<PreviousUntilLastClause> | <PreviousClause>) RBRACKET FloatClause: FLOAT LBRACKET (<PreviousUntilLastClause> | <PreviousClause>) RBRACKET DoubleClause: DOUBLE LBRACKET (<PreviousUntilLastClause> | <PreviousClause>) RBRACKET BoolClause: BOOLEAN LBRACKET (<PreviousUntilLastClause> | <PreviousClause>) RBRACKET TextClause: TEXT LBRACKET (<PreviousUntilLastClause> | <PreviousClause>) RBRACKET PreviousClause : PREVIOUS PreviousUntilLastClause : PREVIOUSUNTILLAST Eg: SELECT last_value(temperature) FROM root.ln.wf01.wt01 GROUP BY([20, 100], 5m) FILL (float[PREVIOUS]) Eg: SELECT last_value(power) FROM root.ln.wf01.wt01 GROUP BY([20, 100], 5m) FILL (int32[PREVIOUSUNTILLAST]) Eg: SELECT last_value(temperature), last_value(power) FROM root.ln.wf01.wt01 GROUP BY([20, 100], 5m) FILL (ALL[PREVIOUS]) difference between PREVIOUSUNTILLAST and PREVIOUS PREVIOUS will fill every interval generated from group by if possible, However, PREVIOUSUNTILLAST will just fill until the last time of the specified time series and the interval after the last time won't be filled and will be null. Note: In group by fill, sliding step is not supported in group by clause Now, only last_value aggregation function is supported in group by fill. Linear fill is not supported in group by fill.