docs: update Flow user guide - #2799
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Signed-off-by: discord9 <discord9@163.com>
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| The clauses must appear in the order shown: `EXPIRE AFTER` comes before `EVAL INTERVAL`. | ||
| `EVAL INTERVAL` schedules repeated evaluation of the full query. Scheduled SQL flows can use joins, |
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EVAL INTERVAL does not schedule every SQL Flow in the current implementation. determine_flow_type still routes non-aggregate/non-DISTINCT SQL to the legacy streaming engine, and that engine explicitly ignores eval_interval; only batching SQL/TQL enters the scheduled loop. A projection or non-aggregate join can therefore accept this clause but still run with streaming semantics instead of periodic full-query evaluation. Please scope this statement to batching SQL (and explain how a query qualifies), or make EVAL INTERVAL force batching before documenting this contract.
| ### Defer creation when a source is missing | ||
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| By default, creating a Flow fails if one of its source tables does not exist. Set | ||
| `defer_on_missing_source` to `true` to persist a pending Flow instead of failing. The Flow is not scheduled while its |
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This reads as though the pending Flow will become scheduled once the table appears. At this head, pending flows are persisted without flownode routes, source-table creation does not revisit them, and pending-to-active CREATE OR REPLACE is explicitly rejected. Please document the actual activation workflow (currently dropping and recreating the Flow after all sources exist) instead of implying automatic activation.
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What changed
EVAL INTERVAL, planner-valid joins, subqueries, SQL CTEs, missing-source deferral, incremental reads, and Flow runtime inspectionupdate_atbehavior for SQL and TQL flowsEXPIRE AFTERscope, stale SQL examples, cleanup commands, and English/Chinese wordingVerified against GreptimeDB
upstream/mainat144f83528db8648bc5607fdc65c249bbfa3c7ffc.Scope
Verification
git diff --checkpnpm buildDOC_LANG=zh pnpm buildDOC_LANG=en pnpm check:linksDOC_LANG=zh pnpm check:linksChecklist