||CDbCommandBuilder provides basic methods to create query commands for tables.
||CDbCriteria represents a query criteria, such as conditions, ordering by,
||CDbExpression represents a DB expression that does not need escaping.
CDbExpression is mainly used in
CActiveRecord as attribute values. When
inserting or updating a
CActiveRecord, attribute values of type
CDbExpression will be directly put into the corresponding SQL statement without
escaping. A typical usage is that an attribute is set with 'NOW()' expression so
that saving the record would fill the corresponding column with the current DB