/** Wraps a relational expression in the projects and filters implied by
* a {@link ModifiableView}.
*
* <p>The input relational expression is suitable for inserting into the view,
* and the returned relational expression is suitable for inserting into its
* delegate table.
*
* <p>In principle, the delegate table of a view might be another modifiable
* view, and if so, the process can be repeated. */
private RelNode createSource(RelOptTable targetTable, RelNode source,
ModifiableView modifiableView, RelDataType delegateRowType) {
final ImmutableIntList mapping = modifiableView.getColumnMapping();
assert mapping.size() == targetTable.getRowType().getFieldCount();
// For columns represented in the mapping, the expression is just a field
// reference.
final Map<Integer, RexNode> projectMap = new HashMap<>();
final List<RexNode> filters = new ArrayList<>();
for (int i = 0; i < mapping.size(); i++) {
int target = mapping.get(i);
if (target >= 0) {
projectMap.put(target, RexInputRef.of(i, source.getRowType()));
}
}
// For columns that are not in the mapping, and have a constraint of the
// form "column = value", the expression is the literal "value".
//
// If a column has multiple constraints, the extra ones will become a
// filter.
final RexNode constraint =
modifiableView.getConstraint(rexBuilder, delegateRowType);
RelOptUtil.inferViewPredicates(projectMap, filters, constraint);
final List<Pair<RexNode, String>> projects = new ArrayList<>();
for (RelDataTypeField field : delegateRowType.getFieldList()) {
RexNode node = projectMap.get(field.getIndex());
if (node == null) {
node = rexBuilder.makeNullLiteral(field.getType());
}
projects.add(
Pair.of(rexBuilder.ensureType(field.getType(), node, false),
field.getName()));
}
return relBuilder.push(source)
.projectNamed(Pair.left(projects), Pair.right(projects), false)
.filter(filters)
.build();
}
ModifiableView
A modifiable view onto ModifiableTable.
It describes how its columns map onto the underlying table's columns, and any constraints that incoming rows must satisfy.
For example, given
CREATE TABLE emps (empno INTEGER, gender VARCHAR(1), deptno INTEGER); CREATE VIEW female_emps AS SELECT empno, deptno FROM emps WHERE gender = 'F';
constraint is $1 = 'F' and column mapping is [0, 2].
NOTE: The current API is inefficient and experimental. It will change without notice.
insert female_emps (empno,gender) values(1,'F')
insert emps (empno,gender) values(SELECT (empno,gender) FROM (empno,gender) values(1,'F') WHERE gender = 'F');
支持的场景比较简单
