zabetak commented on a change in pull request #1020: [CALCITE-2812] Add
algebraic operators to allow expressing recursive queries (Ruben Quesada Lopez)
URL: https://github.com/apache/calcite/pull/1020#discussion_r276292360
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File path: core/src/main/java/org/apache/calcite/tools/RelBuilder.java
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@@ -1705,6 +1711,61 @@ public RelBuilder minus(boolean all, int n) {
return setOp(all, SqlKind.EXCEPT, n);
}
+ /**
+ * Creates a {@link LogicalTableScan} on a {@link TransientTable} (used e.g.
to accumulate
+ * results in repeat union operation), using as its row type the top of the
stack's row type.
+ * Returns this builder.
+ */
+ @Experimental
+ public RelBuilder transientScan(String tableName) {
+ return this.transientScan(tableName, this.peek().getRowType());
+ }
+
+ /**
+ * Creates a {@link LogicalTableScan} on a {@link TransientTable} (used e.g.
to accumulate
+ * results in repeat union operation).
+ * Returns this builder.
+ * @param tableName table name
+ * @param rowType row type of the table
+ */
+ @Experimental
+ public RelBuilder transientScan(String tableName, RelDataType rowType) {
+ TransientTable transientTable = new TransientTable(tableName, rowType);
+ RelOptTable relOptTable = RelOptTableImpl.create(
+ relOptSchema,
+ rowType,
+ transientTable,
+ ImmutableList.of(tableName));
+ RelNode scan = scanFactory.createScan(cluster, relOptTable);
+ push(scan);
+ rename(rowType.getFieldNames());
+ return this;
+ }
+
+ /**
+ * Creates a {@link LogicalRepeatUnion} with no maxRep, i.e.
repeatUnion(tableName, -1).
+ * @param tableName transient table name associated to the repeat union
+ */
+ @Experimental
+ public RelBuilder repeatUnion(String tableName) {
+ return this.repeatUnion(tableName, -1);
+ }
+
+ /**
+ * Creates a {@link LogicalRepeatUnion} of the two most recent relational
expressions
+ * on the stack. Warning: if these relational expressions are not correctly
defined,
+ * this operation might lead to an infinite loop.
+ * Returns this builder.
+ * @param tableName transient table name associated to the repeat union
+ * @param maxRep maximum number of iterations, -1 means no limit
+ */
+ @Experimental
+ public RelBuilder repeatUnion(String tableName, int maxRep) {
+ RelNode iter = LogicalTableSpool.create(build(), Spool.Type.LAZY,
Spool.Type.LAZY, tableName);
Review comment:
I guess it is convenient for the end-users to not have to build separately
the spool when they want to perform the classical recursive union but this
limits a bit the capabilities of the builder. It may be better to provide a
separate method spool to do this. Clients who are only interested for this
use-case can build the utility methods themselves.
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