Design | Architecture and Data Blog

Nulls need special love

The following SELECT statement in code

stmt = DB.prepare("select id,name,state,zip " +
        "from customer " +
        "where " +
        "phone = ? " +
        "and active = ?");
stmt.setString(1, customerPhone);
stmt.setBoolean(2, isActive);
stmt.execute();

where customerPhone and isActive are values you would pass in to the SELECT before its executed. Everything is fine when one day the value passed for customerPhone is NULL. For a database (Oracle is what I know most) a NULL will never be equal to NULL , the SELECT will not return rows where the customer.phone is NULL, leading to wrong results. The SELECT will have to be changed to

Posted by Pramod Sadalage on Thursday, February 15, 2007

Implementing Make Column Non Nullable

While working on a Legacy Application with Legacy Database design as part of fixing a bug, I thought this bug would not have ever happened if a particular column was defined as Non Nullable since this particular column was the identifier to the parent table.

We had a Customer table and the all the names a customer could have like LegalName, LongName, ShortName etc are stored in the CustomerName table. CustomerName cannot exist without Customer hence its logical that the CustomerName.CustomerID column cannot be nullable and should also have a Foreign Key constraint enforcing the relationship. Implementing just the Foreign Key constraint is not enough since the application could potentially be inserting null values in the CustomerName.CustomerID creating orphan records.

Posted by Pramod Sadalage on Friday, December 15, 2006

To allow NULLs or NOT

When to allow NULLs or NOT, is critical domain discussion

Database designs I have seen tend to not constrain the data in the database. For example make the Item.ManufacturerID non-nullable and make it a foreign key to the Manufacturer table. Similarly Manufacturer.Name and Item.Rate as non-nullable columns. In any greenfield application (existing production application is a topic for another post). When you design table(s) lets say you have Item and Manufacturer table as shown below

CREATE TABLE Item
(ItemID NUMBER NOT NULL,
ManufacturerID NUMBER,
Name VARCHAR2(128),
Rate NUMBER,
CONSTRAINT PK_ITEM
              PRIMARY KEY (ItemID)
);

CREATE TABLE Manufacturer
(ManufacturerID NUMBER NOT NULL,
Name VARCAHR2(128),
CONSTRAINT PK_MANUFACTURER
              PRIMARY KEY (ManufacturerID)
);

For now let’s talk about NOT NULL constraint. Many say they don’t make columns non-nullable, because they don’t know the requirements at design time, or they don’t want their tests to create elaborate sets of data, or that the application enforces the constraint then why enforce the constraint on the database?

Posted by Pramod Sadalage on Wednesday, February 8, 2006

Nulls need special love

Implementing Make Column Non Nullable

To allow NULLs or NOT

When to allow NULLs or NOT, is critical domain discussion

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