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Join two tables (left, right) basd on a matching input field (left.inputField = right.lookupField) and add a fetchField column to the first (left) table. This operator is useful if the input table has numerous columns, which can make it difficult to use a simple join.

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Input
table A with (f1, f2, f3) columns,

LQL command

B = select f1 as u1, SIZE(f2) + SIZE(f3) as val from A
C = lookupOperator(A,"f1", B, "u1", "val")

-- C should be a table A with additional "val" column

-- The operator should produce the same output as
-- select f1, f2, f3, val from A join B on A.f1 = B.u1

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