Knut Anders Hatlen created DERBY-6566:
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Summary: Simplify handling of untyped nulls in CASE and NULLIF
expressions
Key: DERBY-6566
URL: https://issues.apache.org/jira/browse/DERBY-6566
Project: Derby
Issue Type: Improvement
Components: SQL
Affects Versions: 11.0.0.0
Reporter: Knut Anders Hatlen
Assignee: Knut Anders Hatlen
Priority: Minor
The parser translates both CASE and NULLIF expressions into ConditionalNodes,
but it represents untyped NULLs differently in the two cases.
In a CASE expression, any branch that is an untyped NULL, is translated into an
UntypedNullConstantNode that's wrapped in a CastNode that casts the value to
CHAR(1). The CastNode is replaced with a cast to the correct type during the
bind phase.
A NULLIF expression is turned into a CASE expression that has a THEN NULL
clause. The parser simply creates an UntypedNullConstantNode for that clause,
without wrapping it in a CastNode. A CastNode is instead added during the bind
phase.
This slight difference in how NULLs are represented by the parser in the two
cases, means that ConditionalNode needs to handle the two cases differently
during the bind phase. It would be better if the parser generated NULLs in the
same way for the two cases, so that ConditionalNode didn't need to know if it
was generated for a CASE expression or a NULLIF expression.
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