findepi commented on code in PR #13240:
URL: https://github.com/apache/datafusion/pull/13240#discussion_r1829086791
##########
datafusion/expr-common/src/signature.rs:
##########
@@ -123,8 +124,19 @@ pub enum TypeSignature {
/// Specifies Signatures for array functions
ArraySignature(ArrayFunctionSignature),
/// Fixed number of arguments of numeric types.
- /// See
<https://docs.rs/arrow/latest/arrow/datatypes/enum.DataType.html#method.is_numeric>
to know which type is considered numeric
+ /// See [`NativeType::is_numeric`] to know which type is considered numeric
+ ///
+ /// [`NativeType::is_numeric`]: datafusion_common
Numeric(usize),
+ /// Fixed number of arguments of numeric types.
+ /// See [`NativeType::is_numeric`] to know which type is considered numeric
+ /// This signature accepts numeric string
+ /// Example of functions In Postgres that support numeric string
+ /// 1. Mathematical Functions, like `abs`
Review Comment:
i confirm this works in PostgreSQL (was testing with PostgreSQL v 17)
```sql
select abs('-123');
```
https://www.postgresql.org/docs/17/typeconv-oper.html#id-1.5.9.7.8 suggests
why this works
'...' is not a varchar literal in PostgreSQL.
it's "unknown-type" literal, which gets interpreted as float8
> Here the system has implicitly resolved the unknown-type literal as type
float8 before applying the chosen operator.
indeed, `select pg_typeof(abs('-123'));` returns `double precision`
However, this doesn't work in PostgreSQL
```sql
select abs(CAST('-123' AS varchar));
```
This fails with "Query Error: function abs(character varying) does not exist"
Indicating that there is no special coercion rules from varchar to numbers
when calling functions like `abs()`.
-----------
BTW, coercion rules can be retrieved from PostgreSQL from
https://www.postgresql.org/docs/17/catalog-pg-cast.html
PostgreSQL doesn't declare any implicit coercions between (selected) numeric
types and (selected) varchar type, and `abs()` function resolution behavior as
described above matches that.
```sql
with selected_types(name) AS (VALUES ('int4'), ('int8'), ('float8'),
('varchar'))
select
src.typname src_type,
dst.typname dst_type,
castcontext,
case castcontext
when 'e' then 'only explicit'
when 'a' then 'explicit | implicitly in assignment'
when 'i' then 'implicitly in expressions, as well as the other cases'
else '???' -- undocumented @
https://www.postgresql.org/docs/17/catalog-pg-cast.html
end castcontext_explained
from pg_cast
join pg_type src on pg_cast.castsource = src.oid
join pg_type dst on pg_cast.casttarget = dst.oid
where true
and src.oid != dst.oid
and src.typname in (select name from selected_types)
and dst.typname in (select name from selected_types)
order by src.typname, dst.typname
;
```
src_type | dst_type | castcontext | castcontext_explained
-- | -- | -- | --
float8 | int4 | a | explicit \| implicitly in assignment
float8 | int8 | a | explicit \| implicitly in assignment
int4 | float8 | i | implicitly in expressions, as well as the other cases
int4 | int8 | i | implicitly in expressions, as well as the other cases
int8 | float8 | i | implicitly in expressions, as well as the other cases
int8 | int4 | a | explicit \| implicitly in assignment
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