Presto 0.217 Documentation

6.5. Conversion Functions

6.5. Conversion Functions

Presto will implicitly convert numeric and character values to the correct type if such a conversion is possible. Presto will not convert between character and numeric types. For example, a query that expects a varchar will not automatically convert a bigint value to an equivalent 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 a varchar to a numeric value type and vice versa.

try_cast(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:

Unit Description Value
B Bytes 1
kB Kilobytes 1024
MB Megabytes 10242
GB Gigabytes 10243
TB Terabytes 10244
PB Petabytes 10245
EB Exabytes 10246
ZB Zettabytes 10247
YB Yottabytes 10248
parse_presto_data_size(string) -> decimal(38)

Parses string of format value unit into a number, where value 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


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