Paul Rogers created IMPALA-7844:
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Summary: Analysis code incorrectly attempts to support ordinals in
HAVING clause
Key: IMPALA-7844
URL: https://issues.apache.org/jira/browse/IMPALA-7844
Project: IMPALA
Issue Type: Bug
Components: Frontend
Affects Versions: Impala 3.0
Reporter: Paul Rogers
Assignee: Paul Rogers
SQL defines the idea of ordinals, which is, apparently, an old way to specify
columns in the {{ORDER BY}} and {{GROUP BY}} clauses:
{code:sql}
SELECT int_col, id
FROM functional.alltypestiny
GROUP BY 1
ORDER BY 2
{code}
The use of an ordinal is semi-ambiguous (is it an ordinal or a literal), but
DBs (including Impala) usually interpret a single integer as an ordinal, but
interpret any expression as a constant. (For example, {{1}} is an ordinal, but
{{2 - 1}} is the constant value 1.)
The use of ordinals works because {{ORDER BY}} and {{GROUP BY}} are lists: it
is clear when an integer stands alone as an ordinal.
The {{HAVING}} (and {{WHERE}}) clauses are expressions. For this reason, DB's
do not support ordinals in these clauses. For example, what is the meaning
below:
{code:sql}
SELECT int_col, id
FROM functional.alltypestiny
WHERE 1 = 2
{code}
Does this mean that the first column equals 2? That the second column equals 1?
The first and second columns are equal? That the constant 1 equals the constant
2?
To avoid such ambiguity, neither the SQL standard nor any implementations
support ordinals in the {{HAVING}} (or {{WHERE}}) clauses.
Yet, [Impala attempts to do
so|https://github.com/apache/impala/blob/master/fe/src/main/java/org/apache/impala/analysis/SelectStmt.java#L549]:
{code:java}
havingPred_ = substituteOrdinalOrAlias(havingClause_, "HAVING",
analyzer_);
{code}
This ticket proposes to remove this code to make it clear that the {{HAVING}}
clause cannot contain an ordinal.
References:
* [Redshift HAVING
clause|https://docs.aws.amazon.com/redshift/latest/dg/r_HAVING_clause.html]
* [Impala
docs|https://impala.apache.org/docs/build3x/html/topics/impala_having.html] are
silent on this question.
* [SQL Standard BNF for
HAVING|https://jakewheat.github.io/sql-overview/sql-2011-foundation-grammar.html#_7_10_having_clause]
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