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https://issues.apache.org/jira/browse/CALCITE-5315?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17615698#comment-17615698
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Stamatis Zampetakis commented on CALCITE-5315:
----------------------------------------------
SQL is declarative but this doesn't mean that there is no ordering between
SELECT, FROM, WHERE, GROUP BY, ORDER BY etc. The SQL semantics would be broken
if order is taken out of the equation.
For the record Postgres, as every other DBMS, clearly defines the order that
the SQL clauses are evaluated:
https://www.postgresql.org/docs/current/sql-select.html
Anyways I agree that this is an edge case so it may not be worth spending too
much time on this.
[~julianhyde] I don't know if the SQL standard says something about projection
pruning although not throwing an error may be a smaller problem. Most likely
users will complain more if their query fails when it was expected to run than
the other way around (complain cause the query doesn't fail).
> Error when pushing filters with operations that may throw (CAST/DIVISION)
> below joins
> -------------------------------------------------------------------------------------
>
> Key: CALCITE-5315
> URL: https://issues.apache.org/jira/browse/CALCITE-5315
> Project: Calcite
> Issue Type: Bug
> Components: core
> Affects Versions: 1.32.0
> Reporter: Stamatis Zampetakis
> Priority: Major
>
> +Steps to reproduce:+
> {code:sql}
> CREATE TABLE emp (empno INT, name VARCHAR, deptno INT);
> INSERT INTO emp VALUES (0, 'Alex', 0);
> INSERT INTO emp VALUES (10, 'Bob', 1);
> CREATE TABLE dept (deptno INT);
> INSERT INTO dept VALUES (1);
> SELECT e.name
> FROM emp e
> INNER JOIN dept d ON e.deptno = d.deptno
> WHERE (10 / e.empno) = 1
> {code}
> *Expected output:*
> Bob
> *Actual output:*
> ERROR: division by zero
> The error is caused when the filter condition in the WHERE clause is
> evaluated before the join. Filter push-down is a very common and powerful
> optimization but when there are operators in the WHERE clause that may throw
> (such as division, cast, etc) this optimization is unsafe and can lead to
> runtime errors.
> The SQL standard (Section 7.4 general rule 1) mandates that WHERE should be
> applied to the result of FROM so in the case above pushing filters below the
> join seems to violate the standard.
> +Citing the standard:+
> "If all optional clauses are omitted, then the result of the <table
> expression> is the same as the result of the
> <from clause>. Otherwise, each specified clause is applied to the result of
> the previously specified clause
> and the result of the <table expression> is the result of the application of
> the last specified clause."
> One of the optional clauses mentioned in the previous paragraph is the
> <where clause>. There seems to be a clearly defined order between the <from
> clause>, which includes inner joins, and the <where clause>.
> Note that this problem is *not* the same as the evaluation order of
> predicates in the WHERE clause, which is implementation specific. This is
> about evaluation order of WHERE clause and FROM clause that is not
> implementation specific.
> Original discussion:
> https://lists.apache.org/thread/cp7h28k1yfxv421q12y1wopbwgrzdzrx
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