system.hypothetical_projections

Description

Lists every hypothetical (what-if) projection defined in the current session. See CREATE HYPOTHETICAL PROJECTION and EXPLAIN WHATIF. The contents are session-scoped: each connection sees only its own hypothetical projections, and the table is empty when none have been created in the current session. The current (database, table) are resolved by UUID at query time, so they reflect RENAME TABLE and entries for dropped tables are hidden automatically.

Columns

database (String) — Database name
table (String) — Table name
name (String) — Projection name
type (Enum8(‘Normal’ = 0, ‘Aggregate’ = 1)) — Projection type
sorting_key (Array(String)) — Projection sorting key
query (String) — Projection SELECT query, empty for the INDEX … TYPE … form
definition (String) — Full projection declaration as written
settings (Map(String, String)) — Projection settings from WITH SETTINGS

Examples

CREATE HYPOTHETICAL PROJECTION p_by_b ON t (SELECT a, b ORDER BY b);
SELECT name, type, sorting_key FROM system.hypothetical_projections;

┌─name───┬─type───┬─sorting_key─┐
│ p_by_b │ Normal │ ['b']       │
└────────┴────────┴─────────────┘

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