具有外连接的 PostgreSQL 时间序列查询

Question

在 PostgreSQL 9.5 数据库中有一个 table metrics_raw 包含各种指标（类型：varchar).
类型是（例如）：TRA、RTC.
我正在执行以下 SQL 以获得年初至今的月度汇总：

SELECT
  count(*),
  "ticks"."ts" AS "timestamp"
FROM
  "metrics_raw"
RIGHT OUTER JOIN
  generate_series('2016-01-01'::timestamp, '2016-10-10'::timestamp, '1 month'::interval) AS ticks(ts)
ON
  "ticks"."ts" = date_trunc('months', "metrics_raw"."timestamp")
WHERE
  "metrics_raw"."type" = 'TRA' OR
  "metrics_raw"."type" IS NULL
GROUP BY "ticks"."ts"
ORDER BY "ticks"."ts"

table 包含一些 TRA 类型的记录（~10 条记录）和 1 个 RTC 类型的记录。
执行 TRA 的查询，我得到 10 行结果符合预期，但对于 RTC 查询，我只得到7 行。还有一件事是没有 RTC 指标我也得到 10 行。

哪里会出错？

Answer 1

感谢@Nemeros，我将查询固定为：

SELECT
  "ticks"."ts" AS "timestamp"
FROM
  generate_series('2016-01-01'::timestamp, '2016-10-10'::timestamp, '1 month'::interval) AS ticks(ts)
LEFT OUTER JOIN
  (
    SELECT *
    FROM "metrics_raw"
    WHERE "metrics_raw"."type" = 'TRA'
  ) as "metrics"
ON
  "ticks"."ts" = date_trunc('months', "metrics"."timestamp")
GROUP BY "ticks"."ts"
ORDER BY "ticks"."ts"

具有外连接的 PostgreSQL 时间序列查询

PostgreSQL timeseries query with outer join

sql

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outer-join