OpenEdge Data Management: DataServer for Microsoft SQL Server

Initial Programming Considerations
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In a DataServer application, you assign the Unknown value (?) to a column by using the
question mark operator (?), which the DataServer translates to the appropriate null-value
representation. For example, the following procedure assigns the Unknown value (?) to the
address2 field of the customer table:
FIND FIRST customer.
customer.address2 = ?.
Zero-length character strings
When you use the Unknown value (?) in a WHERE clause with the DataServer, the Unknown
value (?) satisfies only the equals (=) or not equal () operator. You can also use a zero-length
character string in a WHERE clause. The Unknown value (?) and zero-length character string are
not the same. The Unknown value (?) translates to a NULL, which is a special marker in a data
source that supports NULLs used to represent missing information. On the other hand,
zero-length strings and blank columns contain actual values. Both of the following statements
find the first customer record with a zero-length string in the address2 field. Notice the space
between the quotation marks in the first statement:
FIND FIRST customer WHERE customer.address2 EQ " ".
FIND FIRST customer WHERE customer.address2 EQ "".
Although “” and “ ” evaluate the same way in a WHERE clause, they have different results when
you use them with the BEGINS function. For example, the following statement retrieves all
customer names except those that have the Unknown value (?):
FOR EACH customer WHERE customer.name BEGINS "":
The following statement uses "" to retrieve only those names that begin with a space:
FOR EACH customer WHERE customer.name BEGINS " ":