Help Center/ GaussDB/ Developer Guide(Distributed_V2.0-2.x)/ SQL Optimization/ Hint-based Tuning/ Scan Operation Hints
Updated on 2025-02-27 GMT+08:00
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Scan Operation Hints

Description

These hints specify a scan operation, which can be tablescan, indexscan, or indexonlyscan.

Syntax

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[no] tablescan|indexscan|indexonlyscan(table [index])

Parameters

  • no indicates that the specified hint will not be used for a join.
  • table specifies the table to be scanned. You can specify only one table. Use a table alias (if any) instead of a table name.
  • index indicates the index for indexscan or indexonlyscan. You can specify only one index.

indexscan and indexonlyscan hints can be used only when the specified index belongs to the table.

Scan operation hints can be used for row-store tables and subquery tables.

Example

To specify an index-based hint for a scan, create an index named i on the i_item_sk column of the item table.

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create index i on item(i_item_sk);

Hint the query plan in Example as follows:

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explain
select /*+ indexscan(item i) */ i_product_name product_name ...

item is scanned based on an index. The optimized plan is as follows:

Parent topic: Hint-based Tuning