[teiid-issues] [JBoss JIRA] (TEIID-2188) When using CONCAT2(x, y), can the source query be changed to not include the CASE statements and let Oracle do the NULL compare
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https://issues.jboss.org/browse/TEIID-2188?page=com.atlassian.jira.plugin...
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Van Halbert commented on TEIID-2188:
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Hm, a paragraph from the oracle docs (last sentence):
Although Oracle treats zero-length character strings as nulls, concatenating a zero-length
character string with another operand always results in the other operand, so null can
result only from the concatenation of two null strings. However, this may not continue to
be true in future versions of Oracle Database. To concatenate an expression that might be
null, use the NVL function to explicitly convert the expression to a zero-length string.
When using CONCAT2(x, y), can the source query be changed to not
include the CASE statements and let Oracle do the NULL compare
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Key: TEIID-2188
URL: https://issues.jboss.org/browse/TEIID-2188
Project: Teiid
Issue Type: Enhancement
Components: Query Engine
Affects Versions: 7.4.4
Reporter: Van Halbert
Assignee: Steven Hawkins
When CONCAT2(x, y) is used, the rewritten query is very verbose in adding a CASE
statement to check for nulls. Can the rewritten query not include the CASE statements and
just let Oracle do the compare, because it can do it more efficiently within the CONCAT
call?
Example:
select concat2(f1,f2) from table1
results in
SELECT c_0 FROM (SELECT CASE WHEN to_char(g_0.f1) IS NULL AND g_0.f2 IS NULL THEN NULL
ELSE concat(nvl(to_char(g_0.f1), ''), nvl(g_0.f2, '')) END AS c_0 FROM
table1 g_0)
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