我对 SQL 还很陌生,我正在尝试研究如何在 postgres 中加速复杂的 SQL 查询,也许是通过改进我对索引的使用。这是查询:
SELECT
(SELECT ev.code FROM classification_item ci, enumeration_value ev
WHERE ev.key_id = :ak_0
AND ci.entry_id = t.id AND ci.value_id = ev.id) AS axis_0,
(SELECT ev.code FROM classification_item ci, enumeration_value ev
WHERE ev.key_id = :ak_1
AND ci.entry_id = t.id AND ci.value_id = ev.id) AS axis_1,
SUM(t.amount) as amount,
(SELECT ev.code FROM classification_item ci, enumeration_value ev
WHERE ev.key_id = :key_time_id
AND ci.entry_id = t.id AND ci.value_id = ev.id) AS time
FROM "entry" t
WHERE t.dataset_id = :dataset_id
AND t.id IN (SELECT ci.entry_id FROM classification_item ci, enumeration_value ev
WHERE ev.key_id = :k_0
AND ev.code = :v_0 AND ci.value_id = ev.id)
GROUP BY time, axis_0, axis_1
这基本上是数据库模式(在 Pylons 中定义):
table_dataset = Table('dataset', meta.metadata,
Column('id', Integer, primary_key=True),
)
table_entry = Table('entry', meta.metadata,
Column('id', Integer, primary_key=True),
Column('dataset_id', Integer, ForeignKey('dataset.id')),
Column('amount', Float()),
)
table_classification_item = Table('classification_item', meta.metadata,
Column('id', Integer, primary_key=True),
Column('entry_id', Integer, ForeignKey('entry.id'), index=True),
Column('value_id', Integer, ForeignKey('enumeration_value.id'), index=True)
)
table_enumeration_value = Table('enumeration_value', meta.metadata,
Column('id', Integer, primary_key=True),
Column('key_id', Integer, ForeignKey('key.id'), index=True),
Column('code', UnicodeText(), index=True),
)
它的索引如下:
"dataset_pkey" PRIMARY KEY, btree (id)
"entry_pkey" PRIMARY KEY, btree (id)
"classification_item_pkey" PRIMARY KEY, btree (id)
"ix_classification_item_entry_id" btree (entry_id)
"ix_classification_item_value_id" btree (value_id)
"enumeration_value_pkey" PRIMARY KEY, btree (id)
"ix_enumeration_value_code" btree (code)
"ix_enumeration_value_key_id" btree (key_id)
我是否缺少任何可以加快查询速度的明显索引?尤其是:
- 我应该使用“聚集”索引吗?
- 我也应该
amount
对进行索引entry
,还是对 没有影响SUM(t.amount) as amount
?
谢谢你的帮助。我知道这是一个非常复杂的问题,所以请告诉我是否可以做些什么来改进它。
- - - 更新 - - - - - - -
EXPLAIN ANALYZE对上述查询的输出。