Multi-Join
The Multi-Join feature joins the unique rows from a set of multiple tables onto a set of common keys.
Unlike most table operations, Multi-Join is not a constituent method of the Table class; instead, it is an external function that takes tables as arguments. Also, unlike most table operations, Multi-Join does not return a table -- it returns a MultiJoinTable object, which in turn uses the table() method to return the underlying table.
Syntax
MultiJoinFactory.of(keys, inputTables...)
MultiJoinFactory.of(columnsToMatch, inputTables...)
MultiJoinFactory.of(multiJoinInputs...)
Parameters
| Parameter | Type | Description |
|---|---|---|
| keys | String[] | A String array containing key column names; e.g., |
| inputTables | Table... | Any number of tables to be joined together. |
| columnsToMatch | String | A list of key columns in string format (e.g., "ResultKey=SourceKey" or "KeyInBoth"). If there is more than one key, they must be separated with commas (e.g., note Like |
| multiJoinInputs | MultiJoinInput... | A list of |
Returns
A MultiJoinTable object.
Examples
In this example, we will create a MultiJoinTable using two keys and a list of three source tables.
// import multijoin classes
import io.deephaven.engine.table.MultiJoinFactory
import io.deephaven.engine.table.MultiJoinTable
// create tables
t1 = newTable(
stringCol("Letter", "A", "B", "C", "D"),
intCol("Number", 1, 2, 3, 4),
)
t2 = newTable(
stringCol("Letter", "C", "B", "D", "A"),
intCol("Number", 6, 7, 8, 9),
)
t3 = newTable(
stringCol("Letter", "D", "C", "A", "B"),
intCol("Number", 9, 8, 7, 6),
)
// create a MultiJoinTable object and join the three tables
MultiJoinTable mtTable = MultiJoinFactory.of("Letter, NumCol=Number", t1, t2, t3)
// access the multijoin object's internal table
result = mtTable.table()
- result
In this example, we will create a MultiJoinTable using a list of MultiJoinInput objects.
// import multijoin classes
import io.deephaven.engine.table.MultiJoinFactory
import io.deephaven.engine.table.MultiJoinTable
import io.deephaven.engine.table.MultiJoinInput
// create tables
t1 = newTable(intCol("C1", 1, 2), intCol("C2", 1, 1), intCol("S1", 10, 11))
t2 = newTable(intCol("C1", 3123, 62364), intCol("C3", 56, 99), intCol("S2", 10, 11))
t3 = newTable(intCol("C1", 44, 3), intCol("C4", 182374, 1231), intCol("S3", 44, 2313))
// create MultiJoinInput objects
mj1 = MultiJoinInput.of(t1, "Key=C1")
mj2 = MultiJoinInput.of(t2, "Key=C1")
mj3 = MultiJoinInput.of(t3, "Key=C1")
// create a MultiJoinTable object
mjTable = MultiJoinFactory.of(mj1, mj2, mj3)
result = mjTable.table()
- result