goldmedal commented on code in PR #13372:
URL: https://github.com/apache/datafusion/pull/13372#discussion_r1880062974
##########
datafusion/expr-common/src/signature.rs:
##########
@@ -138,6 +141,48 @@ pub enum TypeSignature {
NullAry,
}
+impl TypeSignature {
+ #[inline]
+ pub fn is_one_of(&self) -> bool {
+ matches!(self, TypeSignature::OneOf(_))
+ }
+}
+
+#[derive(Debug, Clone, Eq, PartialOrd)]
+pub enum TypeSignatureClass {
+ Timestamp,
Review Comment:
Maybe we can refer to the behavior of `Postgres` or `DuckDB`. I listed the
signature of the timestamp function `age` from their system catalogs for
reference.
### Postgres
```sql
test=# SELECT proname, proargtypes FROM pg_proc WHERE proname = 'age';
proname | proargtypes
---------+-------------
age | 28
age | 1114
age | 1184
age | 1114 1114
age | 1184 1184
(5 rows)
test=# SELECT oid, typname FROM pg_type WHERE oid IN (28, 1184, 1114);
oid | typname
------+-------------
28 | xid
1114 | timestamp
1184 | timestamptz
(3 rows)
```
### DuckDB
```sql
D SELECT function_name, parameter_types
FROM duckdb_functions()
WHERE function_name = 'age';
┌───────────────┬──────────────────────────────────────────────────────┐
│ function_name │ parameter_types │
│ varchar │ varchar[] │
├───────────────┼──────────────────────────────────────────────────────┤
│ age │ [TIMESTAMP] │
│ age │ [TIMESTAMP, TIMESTAMP] │
│ age │ [TIMESTAMP WITH TIME ZONE, TIMESTAMP WITH TIME ZONE] │
│ age │ [TIMESTAMP WITH TIME ZONE] │
└───────────────┴──────────────────────────────────────────────────────┘
```
If you try to input an unsupported type value, you may encounter an error
like the following:
```sql
D SELECT age('2001-01-01 18:00:00');
Binder Error: Could not choose a best candidate function for the function
call "age(STRING_LITERAL)". In order to select one, please add explicit type
casts.
Candidate functions:
age(TIMESTAMP WITH TIME ZONE) -> INTERVAL
age(TIMESTAMP) -> INTERVAL
LINE 1: SELECT age('2001-01-01 18:00:00');
```
Both systems treat `TIMESTAMP` and `TIMESTAMP WITH TIME ZONE` as distinct
types in the high level.
The advantage of separating these types is that it allows for stricter
type-checking when matching a function's signature. This reduces the likelihood
of developers failing to correctly handle type checks when implementing
timestamp functions.
Honestly, I'm not sure how complex it would become if we separated them 🤔 .
If it requires significant effort, I'm fine with keeping the current design.
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