Postgres 中的 GROUP BY - JSON 数据类型不相等？

Question

我在比赛中有以下数据 table:

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 select table 中每个最后一个不同的团队的名字。即我想要一个 return:

的查询

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

因此上次该团队出现在 table 中的每个团队。
我一直在使用以下内容（来自 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';

但是这个 returns:

ERROR: could not identify an equality operator for type json
SQL state: 42883
Character: 1680

我了解 Postgres doesn't have equality for JSON。我只需要队名（字符串）相等，不需要比较该队的球员。

任何人都可以建议另一种方法吗？
供参考：

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

returns:

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 text 并跟随 this question，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;

Returns我上面想要的。有人有更好的解决方案吗？

Answer 1

LATERAL 连接更短、更快、更优雅：

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"

如果您只想要不同的团队，ORDER BY 可以。相关：

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

JSON 和相等

Postgres 中 json 数据类型没有相等运算符，但 jsonb (Postgres 9.4+) 有一个：

How to query a json column for empty objects?

Postgres 中的 GROUP BY - JSON 数据类型不相等？

GROUP BY in Postgres - no equality for JSON data type?

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greatest-n-per-group

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JSON 和相等