src/sydra/query/plan.zig

Purpose

Builds a logical plan from the sydraQL AST (ast.zig).

Logical plans are later optimized and lowered into a physical plan.

See also

• Validator (ensures the AST is semantically valid)
• Optimizer
• Physical plan builder
• Operator pipeline

Definition index (public)

pub const BuildError = error { ... }

• UnsupportedStatement — currently only SELECT is supported by the logical planner

pub const Node = union(enum)

Logical node kinds:

• scan
• filter
• project
• aggregate
• sort
• limit

pub const ColumnInfo = struct { ... }

• name: []const u8
• expr: *const ast.Expr

This is the “schema” that flows through planning and execution.

pub const RollupHint = struct { ... }

• bucket_expr: *const ast.Expr — currently used to mark time_bucket(...) grouping expressions

pub fn nodeOutput(node: *Node) []const ColumnInfo

Returns the output schema for a node.

pub const Builder

Fields:

• allocator: std.mem.Allocator
• column_counter: usize = 0 — used to generate stable column names across multiple SELECT lists

Key methods:

• Builder.init(allocator)
• build(statement) – currently supports SELECT only

Key behaviors (as implemented)

• Builds a default scan schema of time and value identifiers.
• Splits WHERE a AND b AND c into Filter.conjunctive_predicates.
• Determines whether aggregation is needed if:
  • any GROUP BY exists, or
  • any projection contains an aggregate/window function (via the function registry).
• Detects a rollup hint when GROUP BY includes time_bucket(...).
• Projection column naming:
  • Uses explicit aliases when present
  • Otherwise uses identifier name, or fnName_<n>, or _col<n>

Node payload structs (public)

Each Node tag has a corresponding payload struct:

• Scan:
  • source: *const ast.Select
  • selector: ?ast.Selector
  • output: []const ColumnInfo
• Filter:
  • input: *Node
  • predicate: *const ast.Expr — combined predicate (may re-build an AND chain)
  • output: []const ColumnInfo
  • conjunctive_predicates: []const *const ast.Expr — flattened AND clauses from the WHERE predicate
• Project:
  • input: *Node
  • projections: []const ast.Projection
  • output: []const ColumnInfo
• Aggregate:
  • input: *Node
  • groupings: []const ast.GroupExpr
  • projections: []const ast.Projection
  • fill: ?ast.FillClause
  • rollup_hint: ?RollupHint
  • output: []const ColumnInfo
• Sort:
  • input: *Node
  • ordering: []const ast.OrderExpr
  • output: []const ColumnInfo
• Limit:
  • input: *Node
  • limit: ast.LimitClause
  • output: []const ColumnInfo

Internal helpers (non-public)

Important builder helpers in the implementation:

• buildSelect — constructs the node chain in this order:
  • scan → optional filter → optional aggregate → project → optional sort → optional limit
• collectPredicates — flattens a AND b binary expressions into a slice
• combinePredicates — rebuilds a single AND-chain expression and unions spans
• inferProjectionName — generates output column names when no alias is provided
• defaultScanColumns — creates synthetic identifier expressions for time and value

Tests

Inline tests cover simple select planning, conjunctive predicates, rollup hints, and alias retention.

Code excerpt

src/sydra/query/plan.zig (node chain + buildSelect excerpt)

pub const Node = union(enum) {
    scan: Scan,
    filter: Filter,
    project: Project,
    aggregate: Aggregate,
    sort: Sort,
    limit: Limit,
};

fn buildSelect(self: *Builder, select: *const ast.Select) (BuildError || std.mem.Allocator.Error)!*Node {
    const projection_columns = try self.buildColumns(select.projections);
    self.column_counter += projection_columns.len;

    const scan_columns = try self.defaultScanColumns();
    var current = try self.makeNode(.{
        .scan = .{
            .source = select,
            .selector = select.selector,
            .output = scan_columns,
        },
    });

    var filter_list = ManagedArrayList(*const ast.Expr).init(self.allocator);
    try self.collectPredicates(select.predicate, &filter_list);
    var filter_conditions: []const *const ast.Expr = &.{};
    if (filter_list.items.len != 0) {
        filter_conditions = try filter_list.toOwnedSlice();
        const predicate = try self.combinePredicates(filter_conditions);
        current = try self.makeNode(.{
            .filter = .{
                .input = current,
                .predicate = predicate,
                .output = nodeOutput(current),
                .conjunctive_predicates = filter_conditions,
            },
        });
    }
    filter_list.deinit();

    if (needsAggregation(select)) {
        const rollup_hint = detectRollupHint(select.groupings);
        current = try self.makeNode(.{
            .aggregate = .{
                .input = current,
                .groupings = select.groupings,
                .projections = select.projections,
                .fill = select.fill,
                .rollup_hint = rollup_hint,
                .output = projection_columns,
            },
        });
    }

    current = try self.makeNode(.{
        .project = .{
            .input = current,
            .projections = select.projections,
            .output = projection_columns,
        },
    });

    return current;
}