Referenced objects in the query are verified and some data type compatibility is checked.
For example, consider the following query:
SELECT * FROM t1 WHERE c1 = 10;
The query normalization stage verifies that table t1 with a column c1 exists in the system tables. It also verifies that the data type of column c1 is compatible with the value 10. If the column's data type is datetime, for example, this statement is rejected.