How Do I Check My Presto Data Type?

Checking the data type of a variable in Presto is an essential task for any developer. It helps us understand the nature of the data we are working with and enables us to make informed decisions about how to handle it. In this tutorial, we will explore different methods to check the data type in Presto, ensuring you have a clear understanding of your data.

Using the typeof() Function

The typeof() function is a convenient way to determine the data type of a variable in Presto. It returns a string representing the data type.

To use the typeof() function, you simply pass your variable as an argument:

SELECT typeof(my_column) FROM my_table;

This query will return the data type of my_column.

Example:

SELECT typeof(42);

This query will return BIGINT, indicating that 42 is an integer.

Casting Using CAST()

If you need to explicitly convert a value to a specific data type, you can use the CAST() function. This function allows you to change the type of a column or expression.

Syntax:
CAST(expression AS datatype)

To check if a column can be casted to another data type, use CAN_CAST():

Syntax:
CAN_CAST(expression AS datatype)

Data Type Conversion:
SELECT CAST('42' AS INTEGER);

This query will convert the string ’42’ to an integer.

Checking if Casting is Possible:
SELECT CAN_CAST('42' AS INTEGER);

This query will return true, indicating that the string ’42’ can be casted to an integer.

Using INFORMATION_SCHEMA.COLUMNS

The INFORMATION_SCHEMA.COLUMNS table provides metadata about columns in your Presto database. By querying this table, you can obtain information about the data type of a specific column.

To check the data type of a column using INFORMATION_SCHEMA.COLUMNS, you need to know the name of the table and column:

SELECT data_type
FROM information_schema.columns
WHERE table_name = 'my_table'
  AND column_name = 'my_column';

Example:

SELECT data_type
FROM information_schema.columns
WHERE table_name = 'users'
  AND column_name = 'age';

This query will return the data type of the age column in the users table.

In Conclusion

In this tutorial, we explored different methods to check the data type in Presto. By using functions like typeof(), CAN_CAST(), and querying the INFORMATION_SCHEMA.COLUMNS, you can easily determine the data type of a variable or column. Understanding your data types is crucial for proper data manipulation and analysis, so make sure to incorporate these techniques into your Presto projects.