Realtime Compute for Apache Flink:Data type conversion

Legacy-Cast behavior

Realtime Compute for Apache Flink enables Legacy-Cast behavior by default. This setting controls how CAST operations behave when a conversion fails.

When table.exec.legacy-cast-behaviour is enabled, a cast from a source data type to a target type may cause precision loss, value overflow, or return null.

CAST and TRY_CAST behavior

CAST

By default (Legacy-Cast enabled), CAST returns null when a conversion exception occurs instead of throwing an error. To make jobs fail explicitly on conversion exceptions, set table.exec.legacy-cast-behaviour=disabled.

CAST('42' AS INT)            -- returns 42 of type INT
CAST(NULL AS VARCHAR)        -- returns NULL of type VARCHAR
-- With table.exec.legacy-cast-behaviour=disabled:
CAST('non-number' AS INT)   -- throws an explicit error

TRY_CAST

TRY_CAST always returns null on conversion exceptions without failing the job. This behavior is equivalent to CAST when table.exec.legacy-cast-behaviour=enabled.

TRY_CAST('42' AS INT)           -- returns 42 of type INT
TRY_CAST(NULL AS VARCHAR)       -- returns NULL of type VARCHAR
TRY_CAST('non-number' AS INT)   -- returns NULL of type INT

Null value handling

To handle null values explicitly, use the cast(null as target_type) syntax. For example:

cast(null as varchar)

This avoids unexpected results such as the "NULL" string or conversion exceptions.