"Conversion" includes, but is not limited to, casting and coercion.
- Casting is explicit conversion and uses the
- Coercion is implicit conversion, which Cloud Dataflow SQL performs automatically under the conditions described below.
The table below summarizes all possible
CAST and coercion possibilities for
Cloud Dataflow SQL data types. "Coercion To" applies to all expressions of a
given data type (e.g. a column)
|From Type||CAST to||Coercion To|
CAST(expr AS typename)
Cast syntax is used in a query to indicate that the result type of an expression should be converted to some other type.
CAST(x=1 AS STRING)
This results in
"false" for any other non-
Casts between supported types that do not successfully map from the original value to the target domain produce runtime errors. For example, casting BYTES to STRING where the byte sequence is not valid UTF-8 results in a runtime error.
When casting an expression
x of the following types, these rules apply:
|From||To||Rule(s) when casting
|INT64||FLOAT64||Returns a close but potentially not exact FLOAT64 value.|
|FLOAT64||STRING||Returns an approximate string representation.
|STRING||BYTES||STRINGs are cast to BYTES using UTF-8 encoding. For example, the STRING "©", when cast to BYTES, would become a 2-byte sequence with the hex values C2 and A9.|
For example, the BYTES literal
An error occurs if
|ARRAY||ARRAY||Must be the exact same ARRAY type.|
|STRUCT||STRUCT||Allowed if the following conditions are met:
Cloud Dataflow SQL coerces the result type of an expression to another type if needed to match function signatures. For example, if function func() is defined to take a single argument of type INT64 and an expression is used as an argument that has a result type of FLOAT64, then the result of the expression will be coerced to INT64 type before func() is computed.