timgrein commented on code in PR #3869:
URL: https://github.com/apache/calcite/pull/3869#discussion_r1687093893
##########
testkit/src/main/java/org/apache/calcite/test/SqlOperatorTest.java:
##########
@@ -10857,6 +10857,7 @@ void assertSubFunReturns(boolean binary, String s, int
start,
f.checkFails("trim('' from 'abcde')",
"Trim error: trim character must be exactly 1 character",
true);
+ f.checkFails("trim()", "String to trim cannot be null", false);
Review Comment:
The creator of the original
https://issues.apache.org/jira/browse/CALCITE-6145 suggested to throw an
exception with an exact description.
I've checked the behavior of PostgreSQL (v15):
```sql
SELECT TRIM() AS trimmed_string;
```
leads to a syntax error: `Query Error: error: syntax error at or near ")"`.
```sql
SELECT TRIM("") AS trimmed_string;
```
leads to an error: `Query Error: error: zero-length delimited identifier at
or near """"`.
```sql
SELECT TRIM(null) AS trimmed_string;
```
returns `null`.
So I think this aligns with the behavior of PostgreSQL throwing an error
during query parsing, _but_ I think the message could be a bit better: `trim
cannot be called without arguments` maybe?
I've added an explicit test for when the value is `null`, which indeed
returns `null` (aligns with PostgreSQL's behavior).
WDYT? @mihaibudiu
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