getLeftStream
Arguments
joinEngine is a table object returned by creating a join engine. The join engines currently supported by DolphinDB are:
createAsofJoinEngine
createEquiJoinEngine
createLookupJoinEngine
createWindowJoinEngine
Details
Return the schema of the left table of the join engine. The data ingested into this schema will be ingested into joinEngine.
The result of an engine can be ingested into the join engine to realize the cascade between engines.
Examples
$ share streamTable(1000:0, `time`sym`price, [TIMESTAMP, SYMBOL, DOUBLE]) as trades
$ output=table(100:0, `timestamp`sym`price1`price2, [TIMESTAMP, SYMBOL, DOUBLE, DOUBLE])
$ leftTable=table(1:0, `sym`timestamp`price, [SYMBOL, TIMESTAMP, DOUBLE])
$ rightTable=table(1:0, `sym`timestamp`price, [SYMBOL, TIMESTAMP, DOUBLE])
$ ajEngine = createAsofJoinEngine("asofjoin_engine", leftTable, rightTable, output, <[leftTable.price, rightTable.price]>, `sym, `timestamp)
$ leftEngine = createReactiveStateEngine(name=`left_reactive_engine, metrics=<[time,msum(price,3)]>, dummyTable=trades, outputTable=getLeftStream(ajEngine), keyColumn="sym")
$ rightEngine = createReactiveStateEngine(name=`right_reactive_engine, metrics=<[time,mfirst(price,3)]>, dummyTable=trades, outputTable=getRightStream(ajEngine), keyColumn="sym")
$ subscribeTable(, "trades", "left_reactive_engine", 0, append!{leftEngine}, true)
$ subscribeTable(, "trades", "right_reactive_engine", 0, append!{rightEngine}, true)
$ t = table(2022.01.01 + 1..20 as time, take(`AMZN`IBM`APPL, 20) as sym, rand(100.0, 20) as price)
$ trades.append!(t)
$ select * from output order by timestamp,sym
timestamp |
sym |
price1 |
price2 |
|---|---|---|---|
2022.01.02T00:00:00.000 |
AMZN |
||
2022.01.03T00:00:00.000 |
IBM |
||
2022.01.04T00:00:00.000 |
APPL |
||
2022.01.05T00:00:00.000 |
AMZN |
||
2022.01.06T00:00:00.000 |
IBM |
||
2022.01.07T00:00:00.000 |
APPL |
||
2022.01.08T00:00:00.000 |
AMZN |
102.192 |
26.2273 |
2022.01.09T00:00:00.000 |
IBM |
152.2704 |
43.6296 |
2022.01.10T00:00:00.000 |
APPL |
126.1056 |
74.929 |
2022.01.11T00:00:00.000 |
AMZN |
137.4656 |
57.6015 |
2022.01.12T00:00:00.000 |
IBM |
116.7775 |
54.2854 |
2022.01.13T00:00:00.000 |
APPL |
58.8909 |
49.3149 |
2022.01.14T00:00:00.000 |
AMZN |
148.5405 |
18.3633 |
2022.01.15T00:00:00.000 |
IBM |
141.0848 |
54.3554 |
2022.01.16T00:00:00.000 |
APPL |
93.9003 |
1.8618 |
2022.01.17T00:00:00.000 |
AMZN |
210.4329 |
61.5008 |
2022.01.18T00:00:00.000 |
IBM |
88.7772 |
8.1367 |
Related function: getRightStream.