Explicit type conversion in postgreSQL - postgresql

Question

I am joining the two tables using the query below:
update campaign_items
set last_modified = evt.event_time
from (
select max(event_time) event_time
,result
from events
where request = '/campaignitem/add'
group by result
) evt
where evt.result = campaign_items.id
where the result column is of character varying type and the id is of integer type
But the data in the result column contains digits(i.e. 12345)
How would I run this query with converting the type of the result(character) into id
(integer)

Answer 1

Well you don't need to because postgresql will do implicit type conversion in this situation. For example, you can try
select ' 12 ' = 12
You will see that it returns true even though there is extra whitespace in the string version. Nevertheless, if you need explicit conversion.
where evt.result::int = campaign_items.id
According to your comment you have values like convRepeatDelay, these obviously cannot be converted to int. What you should then do is convert your int to char!!
where evt.result = campaign_items.id::char

Answer 2

There are several solutions. You can use the cast operator :: to cast a value from a given type into another type:
WHERE evt.result::int = campaign_items.id
You can also use the CAST function, which is more portable:
WHERE CAST(evt.result AS int) = campaign_items.id
Note that to improve performances, you can add an index on the casting operation (note the mandatory double parentheses), but then you have to use GROUP BY result::int instead of GROUP BY result to take advantage of the index:
CREATE INDEX i_events_result ON events_items ((result::int));
By the way the best option is maybe to change the result column type to int if you know that it will only contain integers ;-)