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Posted to dev@iotdb.apache.org by 田原 <ti...@mails.tsinghua.edu.cn> on 2020/02/21 11:26:24 UTC
Group BY Fill Syntax

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.