PostgreSQL:索引时间戳的日期部分

Question

请考虑下表:

       Column       |           Type           |
--------------------+--------------------------+
 id                 | bigint                   |
 creation_time      | timestamp with time zone |
...

像下面这样的查询(更不用说更复杂的JOIN)需要相当长的时间,因为它们需要为每个项计算creation_time :: DATE:

SELECT creation_time::DATE, COUNT(*) FROM items GROUP BY 1;

如何在时间戳的那一天创建索引 - creation_time::DATE？

我试过了:

• CREATE INDEX items_day_of_creation_idx ON items (creation_time)::date;
• CREATE INDEX items_day_of_creation_idx ON items (creation_time::date);

但都失败了:

ERROR:  syntax error at or near "::"

Answer 1

在表达式上创建索引时,必须在括号之间放置表达式(除了围绕列/表达式列表的括号外:

CREATE INDEX items_day_of_creation_idx ON items ( (creation_time::date) );