如何使用 Presto 从 varchar 日期字段中提取日/月/年等？

Question

I currently have tables with dates, set up as VARCHAR in the format of YYYY-MM-DD such as:

2017-01-01

The date column I'm working with is called 'event_dt'

I'm used to being able to use day(event_dt), month(event_dt), year(event_dt) etc. in Hive, but Presto just gives me error executing query with no other explanation when the queries fail.

So, for example, I've tried:

select
month(event_dt)
from
my_sql_table
where
event_dt = '2017-01-01'

I would expect the output to read:

01

but all I get is [Code: 0, SQL State: ] Error executing query

I've tried a few other methods listed in the Presto documentation but am having no luck at all. I realize this is probably very simple but any help would be much appreciated.

Answer 1

You can use themonth() function after converting the varchar to a date with the date() function:

presto> select month(date('2017-01-01'));
 _col0
-------
     1
(1 row)

Answer 2

Thanks to @LukStorms in the comments to the original question, I've found two solutions:

1. Using month(cast(event_dt as date))
2. Using month(date(event_dt))