Postgres中的sql – GROUP BY – JSON数据类型不相等?

我在匹配表中有以下数据:

5;{"Id":1,"Teams":[{"Name":"TeamA","Players":[{"Name":"AAA"},{"Name":"BBB"}]},{"Name":"TeamB","Players":[{"Name":"CCC"},{"Name":"DDD"}]}],"TeamRank":[1,2]}
6;{"Id":2,"Teams":[{"Name":"TeamA","Players":[{"Name":"CCC"},{"Name":"BBB"}]},{"Name":"TeamB","Players":[{"Name":"AAA"},{"Name":"DDD"}]}],"TeamRank":[1,2]}

我想选择每个最后一个不同的团队在他们的名字.即我想要一个返回的查询:

6;{"Name":"TeamA","Players":[{"Name":"CCC"},{"Name":"BBB"}
6;{"Name":"TeamB","Players":[{"Name":"AAA"},{"Name":"DDD"}

所以每个团队从上次那个团队出现在表中.
我一直在使用以下(从here):

WITH t AS (SELECT id, json_array_elements(match->'Teams') AS team FROM matches)
SELECT MAX(id) AS max_id, team FROM t GROUP BY team->'Name';

但这返回:

06003

我明白Postgres doesn’t have equality for JSON.我只需要平等的球队名称(一个字符串),那个球队的球员不需要比较.

任何人都可以提出替代方法来做到这一点吗?
以供参考:

SELECT id, json_array_elements(match->'Teams') AS team FROM matches

收益:

5;"{"Name":"TeamA","Players":[{"Name":"AAA"},{"Name":"BBB"}]}"
5;"{"Name":"TeamB","Players":[{"Name":"CCC"},{"Name":"DDD"}]}"
6;"{"Name":"TeamA","Players":[{"Name":"CCC"},{"Name":"BBB"}]}"
6;"{"Name":"TeamB","Players":[{"Name":"AAA"},{"Name":"DDD"}]}"

编辑:我转换为文本,this question后,我使用DISTINCT ON而不是GROUP BY.这是我的完整查询:

WITH t AS (SELECT id, json_array_elements(match->'Teams') AS team
           FROM matches ORDER BY id DESC)
SELECT DISTINCT ON (team->>'Name') id, team FROM t;

返回上面我想要的有没有人有更好的解决方案?

最佳答案
更加快速,更优雅的LATERAL加入:

SELECT DISTINCT ON (t.team->>'Name') t.team
FROM   matches m, json_array_elements(m.match->'Teams') t(team);
ORDER  BY t.team->>'Name', m.id DESC;  -- to get the "last"

如果你只想要不同的团队,ORDER BY可以去.有关:

> Query for element of array in JSON column
> Query for array elements inside JSON type

JSON和平等

在Postgres中没有json数据类型的等号运算符,但jsonb(Postgres 9.4)有一个:

> How to query a json column for empty objects?

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