postgres 在 json 值匹配 LIKE 条件时查询计数

Question

I have mssql query which works to query the json data which kept in database column like below:

SELECT COUNT(*) as count FROM t1.test where lower(data) LIKE '%state':'new%'

{
  "id": "DO-Test CC1",
  "state": "NEW",
  "type": "Test type",
  "items": [
    {
      "itemReports": [],
      "id": "066c7499-a4b6-4346-ac98-6a71d0ddfc36",
      "itemId": "Augmentn New",
      "quantity": 100,
      "dispenseAsWritten": false,
      "administrationInstructions": "123"
    }
  ]
}

It does not work when i run it at pgAdmin (postgres database).

i am using Docker version 19.03.4, build 9013bf5

which syntax should be replaced?

Answer 1

You don't need to use like or anything similar. You can use ->> to access the value of a key. If you don't know if it's upper or lower case, you can apply a lower() on the result of that expression:

SELECT COUNT(*) as count 
FROM t1.test 
where lower(data ->> 'state') = 'new';

---

If the column is defined as jsonb (which it should be) and you have a GIN index on the data column and you are sure that the state is always upper case, the following is probably more efficient:

SELECT COUNT(*) as count 
FROM t1.test 
where data @> '{"state": "NEW"}'

---

Update as you don't store your JSON in a jsonb column (which you should do), you need to cast the column to jsonb in order to be able to use the functions, eg

where lower(data::jsonb ->> 'state') = 'new';

or

where data::jsonb @> '{"state": "NEW"}

But you should really consider to change that column to jsonb rather than varchar

Answer 2

You can use the ->> JSON operator to access state 's value as text .

SELECT ...
       FROM ...
       WHERE data->>'state' = 'NEW';