7.5. 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.

• 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:

• parse_presto_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