更新时间：2024-11-01 GMT+08:00
案例：建立合适的索引
现象描述
查询与销售部所有员工的信息：
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--建表 CREATE TABLE staffs (staff_id NUMBER(6) NOT NULL, first_name VARCHAR2(20), last_name VARCHAR2(25), employment_id VARCHAR2(10), section_id NUMBER(4), state_name VARCHAR2(10), city VARCHAR2(10)); CREATE TABLE sections(section_id NUMBER(4), place_id NUMBER(4), section_name VARCHAR2(20)); CREATE TABLE states(state_id NUMBER(4)); CREATE TABLE places(place_id NUMBER(4), state_id NUMBER(4)); --优化前查询 EXPLAIN SELECT staff_id,first_name,last_name,employment_id,state_name,city FROM staffs,sections,states,places WHERE sections.section_name='Sales' AND staffs.section_id = sections.section_id AND sections.place_id = places.place_id AND places.state_id = states.state_id ORDER BY staff_id; --创建索引 CREATE INDEX loc_id_pk ON places(place_id); CREATE INDEX state_c_id_pk ON states(state_id); --优化后查询 EXPLAIN SELECT staff_id,first_name,last_name,employment_id,state_name,city FROM staffs,sections,states,places WHERE sections.section_name='Sales' AND staffs.section_id = sections.section_id AND sections.place_id = places.place_id AND places.state_id = states.state_id ORDER BY staff_id; |
优化分析
在优化前，没有创建places.place_id和states.state_id索引，执行计划如下：
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id | operation | E-rows | E-width | E-costs ----+--------------------------------------------------------------+--------+---------+--------- 1 | -> Streaming (type: GATHER) | 2 | 254 | 54.08 2 | -> Sort | 2 | 254 | 53.90 3 | -> Nested Loop (4,5) | 2 | 254 | 53.88 4 | -> Seq Scan on staffs | 20 | 266 | 13.13 5 | -> Materialize | 4 | 12 | 40.37 6 | -> Streaming(type: BROADCAST) | 4 | 12 | 40.36 7 | -> Nested Loop (8,9) | 2 | 12 | 40.20 8 | -> Seq Scan on states | 20 | 12 | 13.13 9 | -> Materialize | 2 | 24 | 26.69 10 | -> Streaming(type: REDISTRIBUTE) | 2 | 24 | 26.68 11 | -> Nested Loop (12,14) | 2 | 24 | 26.57 12 | -> Streaming(type: REDISTRIBUTE) | 1 | 24 | 13.28 13 | -> Seq Scan on sections | 1 | 24 | 13.16 14 | -> Seq Scan on places | 20 | 24 | 13.13 (14 rows) Predicate Information (identified by plan id) ---------------------------------------------------------------- 3 --Nested Loop (4,5) Join Filter: (sections.section_id = staffs.section_id) 7 --Nested Loop (8,9) Join Filter: (places.state_id = states.state_id) 11 --Nested Loop (12,14) Join Filter: (sections.place_id = places.place_id) 13 --Seq Scan on sections Filter: ((section_name)::text = 'Sales'::text) (8 rows) |
建议在places.place_id和states.state_id列上建立2个索引（参考现象描述），执行计划如下：
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id | operation | E-rows | E-width | E-costs ----+---------------------------------------------------------------------+--------+---------+--------- 1 | -> Streaming (type: GATHER) | 2 | 254 | 42.26 2 | -> Sort | 2 | 254 | 42.08 3 | -> Nested Loop (4,5) | 2 | 254 | 42.06 4 | -> Seq Scan on staffs | 20 | 266 | 13.13 5 | -> Materialize | 4 | 12 | 28.55 6 | -> Streaming(type: BROADCAST) | 4 | 12 | 28.54 7 | -> Nested Loop (8,13) | 2 | 12 | 28.38 8 | -> Streaming(type: REDISTRIBUTE) | 2 | 24 | 21.66 9 | -> Nested Loop (10,12) | 2 | 24 | 21.56 10 | -> Streaming(type: REDISTRIBUTE) | 1 | 24 | 13.28 11 | -> Seq Scan on sections | 1 | 24 | 13.16 12 | -> Index Scan using loc_id_pk on places | 1 | 24 | 8.27 13 | -> Index Only Scan using state_c_id_pk on states | 1 | 12 | 3.35 (13 rows) Predicate Information (identified by plan id) ---------------------------------------------------------------- 3 --Nested Loop (4,5) Join Filter: (sections.section_id = staffs.section_id) 11 --Seq Scan on sections Filter: ((section_name)::text = 'Sales'::text) 12 --Index Scan using loc_id_pk on places Index Cond: (place_id = sections.place_id) 13 --Index Only Scan using state_c_id_pk on states Index Cond: (state_id = places.state_id) (8 rows) |
父主题： 实际调优案例
