Temporal Table Function

Unlike a versioned table, temporal table functions can only be defined on top of append-only streams — it does not support changelog inputs. Additionally, a temporal table function cannot be defined in pure SQL DDL.

Temporal table functions can be defined on top of append-only streams using the Table API. The table is registered with one or more key columns, and a time attribute used for versioning.

Suppose we have an append-only table of currency rates that we would like to register as a temporal table function.

Java

TemporalTableFunction rates = tEnv
    .from("currency_rates").
    .createTemporalTableFunction("update_time", "currency");

Scala

Temporal Table Function Join

Once defined, a temporal table function is used as a standard table function. Append-only tables (left input/probe side) can join with a temporal table (right input/build side), i.e., a table that changes over time and tracks its changes, to retrieve the value for a key as it was at a particular point in time.

SELECT * FROM orders;
order_time amount currency
========== ====== =========
10:30        1    USD
10:32       50    Yen
10:52        3    Euro
11:04        5    USD

Given these tables, we would like to convert orders to a common currency — USD.

SQL

Java

Table result = orders
    .select($("(o_amount * r_rate).sum as amount"));