6.5. Conversion Functions

Presto will implicitly convert numeric and character values to thecorrect type if such a conversion is possible. Presto will not convertbetween character and numeric types. For example, a query that expectsa varchar will not automatically convert a bigint value to anequivalent varchar.

When necessary, values can be explicitly cast to a particular type.

Conversion Functions

• cast(value AS type) → type

• Explicitly cast a value as a type. This can be used to cast avarchar to a numeric value type and vice versa.

• trycast(_value AS type) → type

• Like cast(), but returns null if the cast fails.

Data Size

The parse_presto_data_size function supports the following units:

• parsepresto_data_size(_string) -> decimal(38)
• Parses string of format value unit into a number, wherevalue is the fractional number of unit values:

SELECT parse_presto_data_size('1B'); -- 1
SELECT parse_presto_data_size('1kB'); -- 1024
SELECT parse_presto_data_size('1MB'); -- 1048576
SELECT parse_presto_data_size('2.3MB'); -- 2411724

Miscellaneous

• typeof(expr) → varchar
• Returns the name of the type of the provided expression:

SELECT typeof(123); -- integer
SELECT typeof('cat'); -- varchar(3)
SELECT typeof(cos(2) + 1.5); -- double