Snowflake嵌套JSON字段解析问题求助

刚接触Snowflake，尝试解析表中attributes列的嵌套JSON并提取属性，但多次尝试后ID和SOURCE字段始终返回null，STATUS字段正常。

attributes列JSON结构 #

{
    "Status": [
        "ACTIVE"
    ],
    "Coverence": [
        {
            "Sub": [
                {
                    "EndDate": [
                        "2020-06-22"
                    ],
                    "Source": [
                        "Test"
                    ],
                    "Id": [
                        "CovId1"
                    ],
                    "Type": [
                        "CovType1"
                    ],
                    "StartDate": [
                        "2019-06-22"
                    ],
                    "Status": [
                        "ACTIVE"
                    ]
                }
            ]
        }
    ]
}

第一次尝试的SQL #

SELECT DISTINCT *
    from
        (
            TRIM(mt."attributes":Status, '[""]')::string as STATUS,
            TRIM(r.value:"Sub"."Id", '[""]')::string as ID,
            TRIM(r.value:"Sub"."Source", '[""]')::string as SOURCE
            from "myTable" mt,
            lateral flatten ( input => mt."attributes":"Coverence", outer => true) r
        )
    GROUP BY
        STATUS,
        ID,
        SOURCE;

第二次尝试的SQL #

SELECT DISTINCT *
    from
        (
            TRIM(mt."attributes":Status, '[""]')::string as STATUS,
            TRIM(r.value:"Id", '[""]')::string as ID,
            TRIM(r.value:"Source", '[""]')::string as SOURCE
            from "myTable" mt,
            lateral flatten ( input => mt."attributes":"Coverence":"Sub", outer => true) r
        )
    GROUP BY
        STATUS,
        ID,
        SOURCE;

问题排查与解决 #

问题根源 #

1. 第一次SQL：仅对Coverence数组做flatten，r.value是包含Sub数组的对象，直接用r.value:"Sub"."Id"无法访问——因为Sub本身是数组，需要再次flatten才能获取内部对象。
2. 第二次SQL：试图直接flatten Coverence":"Sub，但Coverence是数组，不能直接通过mt."attributes":"Coverence":"Sub"定位到Sub数组，必须先flatten Coverence。
3. 用TRIM去除[""]的方式不够可靠，Snowflake有更直接的数组元素提取方法。

正确SQL示例 #

SELECT DISTINCT
    mt."attributes":Status[0]::string AS STATUS,
    sub_item.value:Id[0]::string AS ID,
    sub_item.value:Source[0]::string AS SOURCE
FROM "myTable" mt
LEFT JOIN LATERAL FLATTEN(input => mt."attributes":Coverence) cov_item
LEFT JOIN LATERAL FLATTEN(input => cov_item.value:Sub) sub_item
GROUP BY STATUS, ID, SOURCE;

关键说明 #

• 分两次flatten：先处理外层的Coverence数组，再处理每个Coverence对象内的Sub数组，逐层拿到目标对象；
• 用[0]直接提取数组第一个元素（你的JSON中每个字段都是单元素数组），比TRIM更稳定；
• 使用LEFT JOIN LATERAL FLATTEN替代隐式逗号连接，逻辑更清晰，也能保留无Coverence数据的行（按需选择）。

内容的提问来源于stack exchange，提问作者Mike