Question

我想使用

SELECT EXTRACT(EPOCH FROM TIMESTAMP '2019-06-01 00:00:00');

可作为独立查询：

postgres=# SELECT EXTRACT(EPOCH FROM TIMESTAMP '2019-06-01 00:00:00');
 date_part
------------
 1559347200
(1 row)

在这样的子查询中：

CREATE TABLE events_201906 PARTITION OF events
    FOR VALUES FROM (SELECT EXTRACT(EPOCH FROM TIMESTAMP '2019-06-01 00:00:00')) TO (SELECT EXTRACT(EPOCH FROM TIMESTAMP '2019-07-01 00:00:00'));

但我不断得到：

ERROR:  syntax error at or near "SELECT"
LINE 2:     FOR VALUES FROM (SELECT EXTRACT(EPOCH FROM TIMESTAMP '20...
                             ^

我在做什么错了？

Answer 1

根据Postgres documentation for CREATE TABLE：

partition_bound_spec 是：

IN ( { numeric_literal | string_literal | TRUE | FALSE | NULL } [, ...] ) |
FROM ( { numeric_literal | string_literal | TRUE | FALSE | MINVALUE | MAXVALUE } [, ...] )
  TO ( { numeric_literal | string_literal | TRUE | FALSE | MINVALUE | MAXVALUE } [, ...] ) | 
WITH ( MODULUS numeric_literal, REMAINDER numeric_literal )

因此它不能是子查询，必须是文字查询。

但是，如果需要，您可以动态执行分区语句，例如：

create or replace function create_partition() returns int as
$fn$
declare
     p_from bigint;
     p_to bigint;
     query text;
begin
   SELECT EXTRACT(EPOCH FROM TIMESTAMP '2019-06-01 00:00:00') into p_from;
   SELECT EXTRACT(EPOCH FROM TIMESTAMP '2019-07-01 00:00:00') into p_to;

   query := 'CREATE TABLE events_201906 PARTITION OF events
             FOR VALUES FROM (' || p_from || ') TO (' || p_to || ');';

   execute query;

   return 1;

end;
$fn$ language plpgsql;

然后执行。当然，您可以通过接受分区名称和时间戳记的参数来使其更有用。

如何使用日期函数作为子查询？

1 个答案: