Question

我正在使用postgres 9.2，而我正在尝试构建一个以特定格式生成json的查询。我已经非常接近一个简单的json_agg表达式，但现在我已经向前移动了。

我有一个简单的三表模式，定义是：

CREATE TABLE project (
    id      INTEGER PRIMARY KEY,
    name    varchar(128) NOT NULL,
    UNIQUE (name)    
);

CREATE TABLE test (
    id          INTEGER PRIMARY KEY,
    name        varchar(128) NOT NULL,
    project_id  integer,
    FOREIGN KEY (project_id) REFERENCES project(id),
);

CREATE TABLE data (
    id              INTEGER PRIMARY KEY,
    date_entered    timestamp with time zone NOT NULL,
    data            json NOT NULL,
    test_id         integer,
    FOREIGN KEY (test_id) REFERENCES test(id)
);

插入一些数据之后：

INSERT INTO project (id, name) VALUES (0, 'my_project');
INSERT INTO test (id, name, project_id) VALUES (0, 'test0', 0);
INSERT INTO data (date_entered, data, test_id) VALUES (TIMESTAMP WITH TIME ZONE '2014-04-15T09:34:41.454999 z', '["some", "data"]', 0);
INSERT INTO test (id, name, project_id) VALUES (1, 'test1', 0);
INSERT INTO data (date_entered, data, test_id) VALUES (TIMESTAMP WITH TIME ZONE '2014-04-15T09:34:41.454999 z', '["some", "data"]', 1);

我想构建一个返回的查询：

{
  "test0": {
    "first_data": "2014-04-15 09:35:10.394+00",
    "data_points": 1
  },
  "test1": {
    "first_data": "2014-04-15 09:35:10.394+00",
    "data_points": 1
  }
}

我最接近这个解决方案的是这个问题：

SELECT
    json_agg(data) as data
FROM (
    SELECT
        test.name as test_name,
        min(data.date_entered) as first_data,
        count(data.id) as data_points
    FROM test
    INNER JOIN data on data.test_id = test.id
    INNER JOIN project on test.project_id = project.id
    WHERE project.name = 'my_project'
    GROUP BY test.name
) as data;

返回：

[
  {
    "test_name":"test0",
    "first_data":"2014-04-15 09:34:41.454999+00",
    "data_points":1
  },
  {
    "test_name":"test1",
    "first_data":"2014-04-15 09:34:41.454999+00",
    "data_points":1
  }
]

我尝试过对row_to_json和array_to_json的各种奇怪用法，但我似乎无法将test_name值转换为外部字典中的键。

这甚至可能吗？我在滥用postgres＆＃39; json生成函数？

Answer 1

使用应用程序语言 jsonifying 确实做得更好。据说这是一个丑陋的字符串连接解决方案

SQL Fiddle

select
    (format(
        '{"%s": {"first_data": "%s", "data_points": %s}}', 
        test.name,
        min(data.date_entered),
        count(data.id)
    ))::json as data
from test
inner join data on data.test_id = test.id
inner join project on test.project_id = project.id
where project.name = 'my_project'
group by test.name

生成json，列值为json dict key

1 个答案: