goldmedal commented on code in PR #13260:
URL: https://github.com/apache/datafusion/pull/13260#discussion_r1830993512
##########
datafusion/optimizer/src/simplify_expressions/expr_simplifier.rs:
##########
@@ -3633,32 +3697,123 @@ mod tests {
#[test]
fn test_like_and_ilke() {
- // LIKE '%'
- let expr = like(col("c1"), "%");
+ let null = lit(ScalarValue::Utf8(None));
+
+ // expr [NOT] [I]LIKE NULL
+ let expr = like(col("c1"), null.clone());
+ assert_eq!(simplify(expr), lit_bool_null());
+
+ let expr = not_like(col("c1"), null.clone());
+ assert_eq!(simplify(expr), lit_bool_null());
+
+ let expr = ilike(col("c1"), null.clone());
+ assert_eq!(simplify(expr), lit_bool_null());
+
+ let expr = not_ilike(col("c1"), null.clone());
+ assert_eq!(simplify(expr), lit_bool_null());
+
+ // expr [NOT] [I]LIKE '%'
+ let expr = like(col("c1"), lit("%"));
+ assert_eq!(simplify(expr), if_not_null(col("c1"), true));
+
+ let expr = not_like(col("c1"), lit("%"));
+ assert_eq!(simplify(expr), if_not_null(col("c1"), false));
+
+ let expr = ilike(col("c1"), lit("%"));
+ assert_eq!(simplify(expr), if_not_null(col("c1"), true));
+
+ let expr = not_ilike(col("c1"), lit("%"));
+ assert_eq!(simplify(expr), if_not_null(col("c1"), false));
+
+ // expr [NOT] [I]LIKE '%%'
Review Comment:
> I thought `expr LIKE '%%'` means the same as `expr = '%'` (match the
actual literal character `%` )
>
> Specifically that `%%` is how to escape the wildcard to not be a wildcard
I think it depends on how we define it. I assume we prefer to follow the
Postgres behavior. 🤔
In Postgres, `%%` doesn't mean matching the actual literal '%'. In Postgres,
the escape character is `\`.
```
test=# select '1' like '%%';
?column?
----------
t
(1 row)
test=# select '%' like '%%';
?column?
----------
t
(1 row)
test=# select '%' like '\%';
?column?
----------
t
(1 row)
test=# select '1' like '\%';
?column?
----------
f
(1 row)
```
I think it is just a redundant wildcard. So, we can simplify it to be only
one `%`.
By the way, in DuckDB, there is a similar behavior for double '%%'.
```
D select '1' like '%%';
┌───────────────┐
│ ('1' ~~ '%%') │
│ boolean │
├───────────────┤
│ true │
└───────────────┘
D select '%' like '%%';
┌───────────────┐
│ ('%' ~~ '%%') │
│ boolean │
├───────────────┤
│ true │
└───────────────┘
````
However, the escape character should be set by `ESCAPE` syntax
```
D select '%' like '\%';
┌───────────────┐
│ ('%' ~~ '\%') │
│ boolean │
├───────────────┤
│ false │
└───────────────┘
D select '%' like '\%' escape '\';
┌──────────────────────────────────┐
│ main.like_escape('%', '\%', '\') │
│ boolean │
├──────────────────────────────────┤
│ true │
└──────────────────────────────────┘
```
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