alamb commented on issue #2890:
URL:
https://github.com/apache/arrow-datafusion/issues/2890#issuecomment-1183077551
@andygrove
I think implict type conversions are needed to do many arithmetic operations
(e.g. adding a float to a integer) and that postgres does add implicit type
conversions. For example:
```sql
alamb=# select cast(1 as smallint) + cast(2 as bigint);
?column?
----------
3
(1 row)
alamb=# select cast(1 as float) + cast(2 as bigint);
?column?
----------
3
(1 row)
```
Postgres also seems to add conversions from integers to string for certain
operations
```sql
alamb=# create table foo(i int, c varchar);
CREATE TABLE
alamb=# insert into foo values (1, 'foo');
INSERT 0 1
alamb=# insert into foo values (2, 'bar');
INSERT 0 1
alamb=# select i || c from foo;
?column?
----------
1foo
2bar
(2 rows)
```
However interestingly it does not seem to try and coerce constants:
```shell
ERROR: invalid input syntax for type integer: "foo"
LINE 1: select 1 = 'foo';
^
alamb=#
```
I suspect postgres doesn't the challenges of equality between strings and
numeric values (e.g. you can't always do it losselessly) -- perhaps we should
remove the automatic string coercion for equality?
I think the code is
https://github.com/apache/arrow-datafusion/blob/6e0bb8476d783c1caaf6bf011487c92ae9352f78/datafusion/expr/src/binary_rule.rs#L167
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