Calcite - Relational Operator (RelNode)
About
Relational Algebra - Expression and Operators in Calcite.
They are used to build a relational expression.
Because of the chaining nature of a relational expression, a relational operator is also a relational expression and share the same interface called RelNode.
Every relational operator (expression) must derive from AbstractRelNode.
Articles Related
List
- Example from RelBuilderExample.java:
Scan
- A scan of the EMP table from the SCOTT schema
final FrameworkConfig config;
final RelBuilder builder = RelBuilder.create(config);
final RelNode node = builder
.scan("EMP")
.build();
System.out.println(RelOptUtil.toString(node));
LogicalTableScan(table=[[scott, EMP]])
- Equivalent to
SELECT *
FROM scott.EMP;
Projection
Calcite - Projection relational operator
Filter and aggregate
final RelNode node = builder
.scan("EMP")
.aggregate(builder.groupKey("DEPTNO"),
builder.count(false, "C"),
builder.sum(false, "S", builder.field("SAL")))
.filter(
builder.call(SqlStdOperatorTable.GREATER_THAN,
builder.field("C"),
builder.literal(10)))
.build();
System.out.println(RelOptUtil.toString(node));
LogicalFilter(condition=[>($1, 10)])
LogicalAggregate(group=[{7}], C=[COUNT()], S=[SUM($5)])
LogicalTableScan(table=[[scott, EMP]])
equivalent to
SELECT deptno, count(*) AS c, sum(sal) AS s
FROM emp
GROUP BY deptno
HAVING count(*) > 10
Multi-join
- The graphical expression tree
join
/ \
join join
/ \ / \
CUSTOMERS ORDERS LINE_ITEMS PRODUCTS
- The tree in calcite
final RelNode left = builder
.scan("CUSTOMERS")
.scan("ORDERS")
.join(JoinRelType.INNER, "ORDER_ID")
.build();
final RelNode right = builder
.scan("LINE_ITEMS")
.scan("PRODUCTS")
.join(JoinRelType.INNER, "PRODUCT_ID")
.build();
final RelNode result = builder
.push(left)
.push(right)
.join(JoinRelType.INNER, "ORDER_ID")
.build();
Values
values(String[] fieldNames, Object... values)
where: fieldName is the name of the columns