Julian Hyde created CALCITE-2914:
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Summary: Improve how LatticeSuggester deduces foreign keys
Key: CALCITE-2914
URL: https://issues.apache.org/jira/browse/CALCITE-2914
Project: Calcite
Issue Type: Bug
Reporter: Julian Hyde
Improve how LatticeSuggester deduces foreign keys.
Currently LatticeSuggester uses SqlStatisticProvider and deduces that a join
between two tables is "many to one" if the left table has more rows than the
right table. Clearly this is wrong, because it does not take into account the
keys of the join.
I think we will change the method
{code:java}
double tableCardinality(List<String> qualifiedTableName){code}
to
{code:java}
double tableCardinality(RelOptTable table){code}
and add a method
{code:java}
boolean isForeignKey(RelOptTable fromTable, List<String> fromColumns,
RelOptTable toTable, List<String> toColumns){code}
For example, {{isForeignKey(empTable, ["DEPTNO"], deptTable, ["DEPTNO"])}}
would return true.
One valid implementation might look at the catalog for foreign key constraints;
another might execute a query to see whether every row in emp is matched by
exaclty one row in dept.
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