I believe the answer is that Oracle is very, very old.
Back in the olden days before there was a SQL standard, Oracle made the design decision that empty strings in VARCHAR
/VARCHAR2
columns were NULL
and that there was only one sense of NULL (there are relational theorists that would differentiate between data that has never been prompted for, data where the answer exists but is not known by the user, data where there is no answer, etc. all of which constitute some sense of NULL
).
By the time that the SQL standard came around and agreed that NULL
and the empty string were distinct entities, there were already Oracle users that had code that assumed the two were equivalent. So Oracle was basically left with the options of breaking existing code, violating the SQL standard, or introducing some sort of initialization parameter that would change the functionality of potentially large number of queries. Violating the SQL standard (IMHO) was the least disruptive of these three options.
Oracle has left open the possibility that the VARCHAR
data type would change in a future release to adhere to the SQL standard (which is why everyone uses VARCHAR2
in Oracle since that data type's behavior is guaranteed to remain the same going forward).
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…