Progress
DataServer for
Microsoft SQL Server
Guide
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:
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:
The following statement uses “ ” to retrieve only those names that begin with a space:
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