Oracle considers empty strings to be NULL while SQL Server does not - how is this best handled?

Question

I have to write a component that re-creates SQL Server tables (structure and data) in an Oracle database. This component also has to take new data entered into the Oracle d

Answer 1

Well, main point I'd consider is absence of tasks when some field can be null, the same field can be empty string and business logic requires to distinguish these values. So I'd make this logic:

• check MSSQL if column has NOT NULL constraint
• check MSSQL if column has CHECK(column <> '') or similar constraint

If both are true, make Oracle column NOT NULL. If any one is true, make Oracle column NULL. If none is true, raise INVALID DESIGN exception (or maybe ignore it, if it's acceptable by this application).

When sending data from MSSQL to Oracle, just do nothing special, all data would be transferred right. When retrieving data to MSSQL, any not-null data should be sent as is. For null strings you should decide whether it should be inserted as null or as empty string. To do this you should check table design again (or remember previous result) and see if it has NOT NULL constraint. If has - use empty string, if has not - use NULL. Simple and clever.

Sometimes, if you work with unknown and unpredictable application, you cannot check for existence of {not empty string} constraint because of various forms of it. If so, you can either use simplified logic (make Oracle columns always nullable) or check whether you can insert empty string into MSSQL table without error.