Merge pull request #4499 from duckdb/revert-4491-struct-cast

Revert "Struct cast changes"

docs/sql/data_types/struct.md

@@ -189,7 +189,7 @@ CREATE TABLE t2 AS SELECT row('a');
 Invalid Input Error: A table cannot be created from an unnamed struct
 ```
 
-When casting between structs, the names of at least one field have to match. Therefore, the following query will fail:
+When casting structs, the names of fields have to match. Therefore, the following query will fail:
 
 ```sql
 SELECT a::STRUCT(y INTEGER) AS b
@@ -198,7 +198,7 @@ FROM
 ```
 
 ```console
-Binder Error: STRUCT to STRUCT cast must have at least one matching member
+Mismatch Type Error: Type STRUCT(x INTEGER) does not match with STRUCT(y INTEGER). Cannot cast STRUCTs - element "x" in source struct was not found in target struct
 ```
 
 A workaround for this is to use [`struct_pack`](#creating-structs) instead:
@@ -267,6 +267,17 @@ These queries return `NULL`.
 SELECT {'k1': 2, 'k2': 3} < {'k1': 2, 'k2': NULL} AS result;
 ```
 
+This query returns a `Binder Error` because the keys do not match positionally.
+
+```sql
+SELECT {'k1': 2, 'k2': 3} < {'k2': 2, 'k1': 4} AS result;
+```
+
+```console
+Binder Error: Cannot compare values of type STRUCT(k1 INTEGER, k2 INTEGER)
+and type STRUCT(k2 INTEGER, k1 INTEGER) - an explicit cast is required
+```
+
 ## Functions
 
 See [Struct Functions]({% link docs/sql/functions/struct.md %}).

docs/sql/data_types/typecasting.md

@@ -99,46 +99,18 @@ Arrays follow the same casting rules as lists. In addition, arrays can be implic
 
 ### Structs
 
-Structs can be cast to other structs as long as they share at least one child element.
-
-> The rationale behind this requirement is to help avoid unintended errors. If two structs do not have any elements in common, then the cast was likely not intended.
+Structs can be cast to other structs as long as the names of the child elements match.
 
 ```sql
 SELECT CAST({'a': 42} AS STRUCT(a VARCHAR));
 ```
 
-Child elements that exist in the target struct, but that do not exist in the source struct, default to `NULL`.
-
-```sql
-SELECT CAST({'a': 42} AS STRUCT(a VARCHAR, b VARCHAR));
-```
-
-Child elements that only exist in the source struct are ignored.
-
-```sql
-SELECT CAST({'a': 42, 'b': 43} AS STRUCT(a VARCHAR));
-```
-
 The names of the struct can also be in a different order. The fields of the struct will be reshuffled based on the names of the structs.
 
 ```sql
 SELECT CAST({'a': 42, 'b': 84} AS STRUCT(b VARCHAR, a VARCHAR));
 ```
 
-Struct casting behaves differently when combined with the [`UNION [ALL] BY NAME`]({% link docs/sql/query_syntax/setops.md %}#union-all-by-name) operation.
-In that case, the fields of the resulting struct are the superset of all fields of the input structs.
-This logic also applies recursively to potentially nested structs.
-
-```sql
-SELECT {'outer1': {'inner1': 42, 'inner2': 42}} AS c
-UNION ALL BY NAME 
-SELECT {'outer1': {'inner2': 'hello', 'inner3': 'world'}, 'outer2': '100'} AS c;
-```
-
-```sql
-SELECT [{'a': 42}, {'b': 84}];
-```
-
 ### Unions
 
 Union casting rules can be found on the [`UNION type page`]({% link docs/sql/data_types/union.md %}#casting-to-unions).