Question

我正在使用SQLite。我有一个查询，经过6个不同的表后得到记录。每个表包含许多记录。下面的查询是基于PK-FK关系编写的，但它需要花费太多时间来检索数据。

我无法对数据库进行更改，索引。

Select distinct A.LINK_ID as LINK_ID,
                B.POI_ID
from RDF_LINK as A,
     RDF_POI as B,
     RDF_POI_ADDRESS as c,
     RDF_LOCATION as d,
     RDF_ROAD_LINK as e,
     RDF_NAV_LINK as f
where B.[CAT_ID] = '5800'
  AND B.[POI_ID] = c.[POI_ID]
  AND c.[LOCATION_ID] = d.[LOCATION_ID]
  AND d.[LINK_ID] = A.[LINK_ID]
  AND A.[LINK_ID] = e.[LINK_ID]
  AND A.[LINK_ID] = f.[LINK_ID]

我使用了错误的方法吗？我需要使用IN吗？

EXPLAIN QUERY PLAN命令输出::

0   0   3   SCAN TABLE RDF_LOCATION AS d (~101198 rows)
0   1   0   SEARCH TABLE RDF_LINK AS A USING COVERING INDEX sqlite_autoindex_RDF_LINK_1 (LINK_ID=?) (~1 rows)
0   2   5   SEARCH TABLE RDF_NAV_LINK AS f USING COVERING INDEX sqlite_autoindex_RDF_NAV_LINK_1 (LINK_ID=?) (~1 rows)
0   3   4   SEARCH TABLE RDF_ROAD_LINK AS e USING COVERING INDEX NX_RDFROADLINK_LINKID (LINK_ID=?) (~2 rows)
0   4   1   SEARCH TABLE RDF_POI AS B USING AUTOMATIC COVERING INDEX (CAT_ID=?) (~7 rows)
0   5   2   SEARCH TABLE RDF_POI_ADDRESS AS c USING COVERING INDEX sqlite_autoindex_RDF_POI_ADDRESS_1 (POI_ID=? AND LOCATION_ID=?) (~1 rows)
0   0   0   USE TEMP B-TREE FOR DISTINCT

Answer 1

AUTOMATIC上有RDF_POI.CAT_ID个索引。这意味着数据库认为为此查询创建临时索引是值得的。您应该永久创建此索引：

CREATE INDEX whatever ON RDF_POI(CAT_ID);

此外，CAT_ID查找似乎没有高选择性。

运行ANALYZE，以便数据库更好地了解数据的形状。

提高查询性能

1 个答案: