Presto: why presto don't support implicit conversion from number to varchar ?

Created on 21 Jun 2018 · 5Comments · Source: prestodb/presto

my create table statement are:

CREATE TABLE `address`(
  `x` int, 
  `y` int);

and when I query use :

    select * from address where x = '1'

I got an exception like

  com.facebook.presto.sql.analyzer.SemanticException: line 1:8: Cannot cast integer to char(1)
    at com.facebook.presto.sql.analyzer.ExpressionAnalyzer$Visitor.visitCast(ExpressionAnalyzer.java:944)
    at com.facebook.presto.sql.analyzer.ExpressionAnalyzer$Visitor.visitCast(ExpressionAnalyzer.java:288)
    at com.facebook.presto.sql.tree.Cast.accept(Cast.java:98)

but. hive support this implicit conversion.
does presto want to do this ? if not , why?
thx !

Source

xingnailu

Most helpful comment

May be all the Hive users want this features. @findepi . It take huge cost changes for rewrite Hive scripts. Hive‘s market is so huge(ETL). Why not consider fully supporting Hive? This is more conducive to the development of Presto. Presto can increase the indication that opening this feature will reduce performance.

hereTac on 14 Sep 2018

👍4

All 5 comments

@xingnailu just curious, what Presto version is this? Mine says line 1:31: '=' cannot be applied to integer, varchar(1) ('a' is currently considered a varchar(1) rather than char(1)).

If there was the implicit conversion integer -> varchar, the end result wouldn't be that nice anyway. Note that operations, including comparisons, on varchars are slower than on numbers.

Of course, this doesn't mean such a coercion should not exist. The SQL standard governs that, but I didn't check it

findepi on 21 Jun 2018

@findepi I am glad to receive you replication. And my presto version is 0.192. Can I consider the reason that presto don't implicit conversion integer to varchar is efficiency. I think I will do this implicit conversion by myself.
thx

xingnailu on 21 Jun 2018