What does the 'UNSUPPORTED_SUBQUERY_EXPRESSION_CATEGORY' error class in Databricks SQL indicate and what are some specific error messages that fall under this category?
The `UNSUPPORTED_SUBQUERY_EXPRESSION_CATEGORY` error class in Databricks SQL indicates that there is an issue with a subquery expression in the SQL query. This error class encompasses various specific error messages related to unsupported subquery expressions, correlated subqueries, and non-equality predicates. Here are some examples of error messages that fall under this category:

1. `ACCESSING_OUTER_QUERY_COLUMN_IS_NOT_ALLOWED`: This error message indicates that accessing an outer query column is not allowed in a specific location in the query.
2. `AGGREGATE_FUNCTION_MIXED_OUTER_LOCAL_REFERENCES`: This error message occurs when an aggregate function in a correlated predicate has both outer and local references, which is not supported.
3. `CORRELATED_COLUMN_IS_NOT_ALLOWED_IN_NON_EQUALITY_PREDICATE`: This error message indicates that a correlated column is not allowed in a non-equality predicate.
4. `CORRELATED_COLUMN_IS_NOT_ALLOWED_IN_PREDICATE`: This error message indicates that a correlated column is not allowed in a predicate.
5. `CORRELATED_COLUMN_NOT_FOUND`: This error message occurs when a correlated outer name reference within a subquery expression body is not found in the enclosing query.
6. `CORRELATED_REFERENCE`: This error message indicates that expressions referencing the outer query are not supported outside of WHERE/HAVING clauses.
7. `LATERAL_JOIN_CONDITION_NON_DETERMINISTIC`: This error message indicates that a lateral join condition cannot be non-deterministic.
8. `MUST_AGGREGATE_CORRELATED_SCALAR_SUBQUERY`: This error message occurs when correlated scalar subqueries must be aggregated to return at most one row.
9. `NON_CORRELATED_COLUMNS_IN_GROUP_BY`: This error message indicates that a GROUP BY clause in a scalar correlated subquery cannot contain non-correlated columns.
10. `NON_DETERMINISTIC_LATERAL_SUBQUERIES`: This error message indicates that non-deterministic lateral subqueries are not supported when joining with outer relations that produce more than one row.
11. `UNSUPPORTED_CORRELATED_REFERENCE_DATA_TYPE`: This error message indicates that a correlated column reference cannot be a specific data type.
12. `UNSUPPORTED_CORRELATED_SCALAR_SUBQUERY`: This error message occurs when correlated scalar subqueries can only be used in filters, aggregations, projections, and UPDATE/MERGE/DELETE commands.
13. `UNSUPPORTED_IN_EXISTS_SUBQUERY`: This error message indicates that IN/EXISTS predicate subqueries can only be used in filters, joins, aggregations, window functions, projections, and UPDATE/MERGE/DELETE commands.
14. `UNSUPPORTED_TABLE_ARGUMENT`: This error message occurs when table arguments are used in a function where they are not supported.