如果字段不为空，则仅提取 json

Question

我想从（可为空的）JSONB 字段中提取键值。如果该字段为 NULL，我希望该记录仍然存在于我的结果集中，但带有一个空字段。

customer表：

id, name, phone_num, address
1, "john", 983, [ {"street":"23, johnson ave", "city":"Los Angeles", "state":"California", "current":true}, {"street":"12, marigold drive", "city":"Davis", "state":"California", "current":false}]
2, "jane", 9389, null
3, "sally", 352, [ "street":"90, park ave", "city":"Los Angeles", "state":"California", "current":true} ]

当前 PostgreSQL 查询：

select id, name, phone_num, items.city
from customer, 
     jsonb_to_recordset(customer) as items(city str, current bool)
where items.current=true

返回：

id, name, phone_num, city
1, "john", 983, "Los Angeles"
3, "sally", 352, "Los Angeles"

所需输出：

id, name, phone_num, city
1, "john", 983, "Los Angeles"
2, "jane", 9389, null
3, "sally", 352, "Los Angeles"

如何实现上述输出？

Answer 1

使用left join lateral 而不是隐式横向连接：

select c.id, c.name, c.phone_num, i.city
from customer c
left join lateral jsonb_to_recordset(c.address) as i(city str, current bool)
    on i.current=true