Postgresql实现递归查询字典并转JSON

现在有一张字典表，有二级 、三级字典项，需要递归查询并转换成JSON对象。字典数据情况如下：

查询语句如下：

WITH RECURSIVE c AS (
    SELECT dictionaries_id,BIANMA,NAME,parent_id, 0 as lvl
    FROM   sys_dictionaries
    WHERE  dictionaries_id ='91f9e33300824f84a2a0b8780775fb2f' AND parent_id='0'
  UNION ALL
    SELECT d.dictionaries_id,d.BIANMA,d.NAME,d.parent_id, c.lvl + 1
    FROM   sys_dictionaries d
    JOIN   c ON d.parent_id = c.dictionaries_id
),
maxlvl AS (
  SELECT max(lvl) maxlvl FROM c
),

j AS (
    SELECT c.*, json '[]' children
    FROM   c, maxlvl
    WHERE  lvl = maxlvl
  UNION ALL
    SELECT   (c).*, array_to_json(array_agg(j) || array(SELECT r
                                                        FROM   (SELECT l.*, json '[]' children
                                                                FROM   c l, maxlvl
                                                                WHERE  l.parent_id = (c).dictionaries_id
                                                                AND    l.lvl < maxlvl
                                                                AND    NOT EXISTS (SELECT 1
                                                                                   FROM   c lp
                                                                                   WHERE  lp.parent_id = l.dictionaries_id)) r)) children
    FROM     (SELECT c, j
              FROM   c
              JOIN   j ON j.parent_id = c.dictionaries_id) v
    GROUP BY v.c
)
SELECT row_to_json(j) json_tree
FROM   j
WHERE  lvl = 0;

查询结果类似这样:

{
    "dictionaries_id": "91f9e33300824f84a2a0b8780775fb2f",
    "bianma": "wp_sjyt",
    "name": "合法图斑实际用途",
    "parent_id": "0",
    "lvl": 0,
    "children": [
        {
            "dictionaries_id": "ca97634ca1ef4ae79d2397d398b75595",
            "bianma": "01",
            "name": "商服用地",
            "parent_id": "91f9e33300824f84a2a0b8780775fb2f",
            "lvl": 1,
            "children": [
                {
                    "dictionaries_id": "b1e11a35b81b49e4a5d4d879d529d2f5",
                    "bianma": "01_07",
                    "name": "其他商服用地",
                    "parent_id": "ca97634ca1ef4ae79d2397d398b75595",
                    "lvl": 2,
                    "children": []
                },
                {
                    "dictionaries_id": "87f5bf6d27e244a5b75c3c46a3ad1e11",
                    "bianma": "01_06",
                    "name": "娱乐用地",
                    "parent_id": "ca97634ca1ef4ae79d2397d398b75595",
                    "lvl": 2,
                    "children": []
                },
                {
                    "dictionaries_id": "0ffbf2c61fee4886881ed9fbf4300a1b",
                    "bianma": "01_05",
                    "name": "商务金融用地",
                    "parent_id": "ca97634ca1ef4ae79d2397d398b75595",
                    "lvl": 2,
                    "children": []
                },
                {
                    "dictionaries_id": "5f74e7d1710c49ef84360d6a7ef5ce2a",
                    "bianma": "01_04",
                    "name": "旅馆用地",
                    "parent_id": "ca97634ca1ef4ae79d2397d398b75595",
                    "lvl": 2,
                    "children": []
                },
                {
                    "dictionaries_id": "0ad1d97089434c6b86b7b256bf572792",
                    "bianma": "01_03",
                    "name": "餐饮用地",
                    "parent_id": "ca97634ca1ef4ae79d2397d398b75595",
                    "lvl": 2,
                    "children": []
                },
                {
                    "dictionaries_id": "e010e20ee128459aa23bceef95d7f6ae",
                    "bianma": "01_02",
                    "name": "批发市场用地",
                    "parent_id": "ca97634ca1ef4ae79d2397d398b75595",
                    "lvl": 2,
                    "children": []
                },
                {
                    "dictionaries_id": "783da69c120c43d4bf23b9ea51ab5033",
                    "bianma": "01_01",
                    "name": "零售商业用地",
                    "parent_id": "ca97634ca1ef4ae79d2397d398b75595",
                    "lvl": 2,
                    "children": []
                }
            ]
        },
        {
            "dictionaries_id": "62fe418f9b084811b86f53f412fb87c1",
            "bianma": "02",
            "name": "工矿仓储用地",
            "parent_id": "91f9e33300824f84a2a0b8780775fb2f",
            "lvl": 1,
            "children": []
        },
        {
            "dictionaries_id": "ea91d0e0035249d29755efbf9e386752",
            "bianma": "03",
            "name": "住宅用地",
            "parent_id": "91f9e33300824f84a2a0b8780775fb2f",
            "lvl": 1,
            "children": []
        },
        {
            "dictionaries_id": "74c1c1571bd9419fa59aa8dd7820bec5",
            "bianma": "04",
            "name": "公共管理与公共服务用地",
            "parent_id": "91f9e33300824f84a2a0b8780775fb2f",
            "lvl": 1,
            "children": []
        },
        {
            "dictionaries_id": "9369c75048aa489697a3242fd854802b",
            "bianma": "05",
            "name": "特殊用地",
            "parent_id": "91f9e33300824f84a2a0b8780775fb2f",
            "lvl": 1,
            "children": []
        },
        {
            "dictionaries_id": "1e05348899754affa2663c31cf9815d3",
            "bianma": "06",
            "name": "交通运输用地",
            "parent_id": "91f9e33300824f84a2a0b8780775fb2f",
            "lvl": 1,
            "children": []
        },
        {
            "dictionaries_id": "752406e52b9e473bb9f858268247a72e",
            "bianma": "07",
            "name": "水域及水利设施用地",
            "parent_id": "91f9e33300824f84a2a0b8780775fb2f",
            "lvl": 1,
            "children": []
        },
        {
            "dictionaries_id": "6ef459de851d48e1aae376150a74747e",
            "bianma": "08",
            "name": "其他土地",
            "parent_id": "91f9e33300824f84a2a0b8780775fb2f",
            "lvl": 1,
            "children": []
        }
    ]
}

标签：Postgresql,递归,parent,dictionaries,children,JSON,lvl,id,name
来源： https://www.cnblogs.com/codefree/p/16023064.html