Yu Tang created CALCITE-6727:
--------------------------------
Summary: Column uniqueness constrain should only apply to inner
join
Key: CALCITE-6727
URL: https://issues.apache.org/jira/browse/CALCITE-6727
Project: Calcite
Issue Type: Bug
Components: core
Affects Versions: 1.38.0
Reporter: Yu Tang
When joining with a singleton relation, the keys from the other side are
considered to be "associative unique".
{code:java}
// RelMdColumnUniqueness.areColumnsUnique(Join rel, RelMetadataQuery mq ...
final Double rightMaxRowCount = mq.getMaxRowCount(right);
if (rightMaxRowCount != null && rightMaxRowCount <= 1.0) {
leftColumns = leftColumns.union(joinInfo.leftSet());
}
final Double leftMaxRowCount = mq.getMaxRowCount(left);
if (leftMaxRowCount != null && leftMaxRowCount <= 1.0) {
rightColumns = rightColumns.union(joinInfo.rightSet());
} {code}
In the case
{code:java}
@Test void testColumnUniquenessForJoinOnLimit1() {
final String sql = ""
+ "select *\n"
+ "from emp A\n"
+ "join (\n"
+ " select * from emp\n"
+ " limit 1) B\n"
+ "on A.empno = B.empno";
sql(sql)
.assertThatAreColumnsUnique(bitSetOf(0), is(true))
.assertThatAreColumnsUnique(bitSetOf(1), is(true))
.assertThatAreColumnsUnique(bitSetOf(9), is(true))
.assertThatAreColumnsUnique(bitSetOf(10), is(true))
.assertThatAreColumnsUnique(bitSetOf(), is(true))
.assertThatUniqueKeysAre(bitSetOf());
} {code}
the join result {{A.ENAME}} is considered to be unique because {{A.EMPNO}} is
the unique key. The test still passes when we change it to left join, in which
case {{A.ENAME}} is not guaranteed to be unique.
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