I have a table with the following schema:

CREATE TABLE [dbo].[Obj1Json](
    [ObjectID] [int] IDENTITY(1,1) NOT NULL,
    [PointerToSource] [nvarchar](255) NULL,
    [CreateDate] [datetime2](7) NOT NULL,
    [ModifiedDate] [datetime2](7) NOT NULL,
    [Indexes] [nvarchar](max) NULL,
    [vAccountID]  AS (json_value([Indexes],'$.AccountID'))

where the Indexes column contains JSON that looks like:

  "AccountID": 73786,
  "AccountName": "5869b4e9-f441-463f-8f6d-93b4f4ff8c75",
  "ProcessLocation": "Start",
  "IsPasswordProtected": true,
  "InvoiceDate": "2020-12-30T09:00:32.8473077-05:00"

The vAccountID column is used for an index on the JSON in Indexes:

ON Obj1Json(vAccountID)

The table has about 10.5 million rows of randomly generated data (all data in the Indexes column has the same structure, however). The query I'm running is

SELECT JSON_VALUE(Indexes, '$.AccountID')
  FROM [Obj1Json]
  WHERE JSON_VALUE(Indexes, '$.AccountID') = 69725

which returns 110 results. When looking at the execution plan in SSMS, I see that an index scan is being used, whereas I would expect an index seek to be used instead.

Query plan of the above query, showing an index scan being used

The query returns quickly (under a second), but I'm curious why an index seek isn't being used. Is there any obvious reason why SQL Server is using an index scan instead of a seek?

  • It is having to implicitly convert the values stored in the index to integers in order to compare them to your input. Perhaps use '69725' instead Jan 5, 2021 at 19:25
  • Just curious why aren't you using your vAccountID column in the WHERE clause of your query anyway?
    – J.D.
    Jan 5, 2021 at 19:32

1 Answer 1


The issue is that JSON_VALUE returns an NVARCHAR and you sent in an INTEGER. This causes a Convert_Implicit.

If you pass in a VARCHAR or NVARCHAR param/value into the WHERE condition, it does a seek and drops the rows read.

  • That did the trick, good catch! Thanks!
    – DylanSp
    Jan 5, 2021 at 19:52
  • 2
    If it's guaranteed to always be an integer, it might be worth it to redefine the column to match, e.g. vAccountID AS CONVERT(int, (JSON_VALUE(Indexes, '$.AccountID'))) Jan 5, 2021 at 21:49
  • @ErikDarling Also good to know, I didn't think of that.
    – DylanSp
    Jan 6, 2021 at 13:23

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