Package dev.frostlake.executor

Class ConnectByExpander

java.lang.Object

dev.frostlake.executor.ConnectByExpander

public final class ConnectByExpander
extends Object

Snowflake hierarchical queries — [START WITH <pred>] CONNECT BY [PRIOR] c = [PRIOR] c.

The expansion walks the FROM clause's rows as a forest: the rows matching START WITH are the roots (without START WITH every row is its own root, live-verified), and a row becomes a child of the row above it whenever the CONNECT BY predicate holds with PRIOR bound to the parent and every other reference bound to the candidate child. Each emitted row carries its own values plus two pseudo-column groups, both hidden from SELECT * exactly as Snowflake hides them:

• LEVEL — 1 for a root, +1 per step down;
• CONNECT_BY_ROOT$<col> — the root row's value of every source column, which is what ConnectByRootExpression reads.

Snowflake applies WHERE to the EXPANDED rows (live-verified: filtering out a parent still keeps its children), so this runs before the WHERE stage and everything downstream sees an ordinary relation.

Snowflake performs no cycle detection — a cyclic hierarchy simply runs until the warehouse times out (live-verified). An in-memory engine cannot hang, so the walk is bounded by MAX_DEPTH, the same guard value the recursive-CTE fixpoint loop uses, and reports the cycle instead.

Field Summary

Fields

Modifier and Type	Field	Description
static final String	LEVEL_COLUMN	The LEVEL pseudo-column's name.
static final int	MAX_DEPTH	Maximum hierarchy depth before the walk is reported as cyclic.
static final String	SHADOWED_LEVEL_COLUMN	The out-of-the-way name a source column called LEVEL takes in the expanded relation, so the name LEVEL resolves to the depth pseudo-column.

Constructor Summary

Constructors

Constructor	Description
ConnectByExpander(QueryExecutor executor, FunctionRegistry functionRegistry, Catalog catalog)

Method Summary

Modifier and Type	Method	Description
List<Row>	expand(List<Row> baseRows, Table baseTable, Table expandedTable, FrostlakeParser.ConnectByClauseContext clause, Map<String,Table> aliasToTable, List<Table> allTables)	Expand baseRows into the hierarchy described by the clause, in depth-first pre-order (parent immediately before its subtree).
Table	expandedTable(Table baseTable)	The relation the expansion produces: the source columns followed by the LEVEL depth pseudo-column and the hidden CONNECT_BY_ROOT$<col> pseudo-columns.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

MAX_DEPTH

public static final int MAX_DEPTH

Maximum hierarchy depth before the walk is reported as cyclic.

See Also:

• Constant Field Values

LEVEL_COLUMN

public static final String LEVEL_COLUMN

The LEVEL pseudo-column's name.

See Also:

• Constant Field Values

SHADOWED_LEVEL_COLUMN

public static final String SHADOWED_LEVEL_COLUMN

The out-of-the-way name a source column called LEVEL takes in the expanded relation, so the name LEVEL resolves to the depth pseudo-column.

See Also:

• Constant Field Values

Constructor Details

ConnectByExpander

public ConnectByExpander(QueryExecutor executor,
 FunctionRegistry functionRegistry,
 Catalog catalog)

Method Details

expandedTable

public Table expandedTable(Table baseTable)

The relation the expansion produces: the source columns followed by the LEVEL depth pseudo-column and the hidden CONNECT_BY_ROOT$<col> pseudo-columns. The pseudo-column SHADOWS a source column of the same name — live, both the bare level and the QUALIFIED t.level answer the depth inside a CONNECT BY query, even over a table whose own LEVEL column holds other values — so a clashing source column is renamed out of resolution here. Without a clash the depth column stays hidden from SELECT *, exactly as before; with one it takes the source column's star slot.

expand

public List<Row> expand(List<Row> baseRows,
 Table baseTable,
 Table expandedTable,
 FrostlakeParser.ConnectByClauseContext clause,
 Map<String,Table> aliasToTable,
 List<Table> allTables)

Expand baseRows into the hierarchy described by the clause, in depth-first pre-order (parent immediately before its subtree). The result's rows match expandedTable(dev.frostlake.metastore.model.Table)'s shape.