Question

Consider this simple table :

table create statement is :

CREATE TABLE [dbo].[Test_Serializable](
[Id] [int] NOT NULL,
[Name] [nvarchar](50) NOT NULL
)

so there is not any primary key or index.

consider it’s emopty and has not any row.I want to Insert this row (1,'nima') but I want to check if there is a row with Id=1 or not.if yes call RAISERROR and if no Insert row.I write this script:

SET TRANSACTION ISOLATION LEVEL SERIALIZABLE
BEGIN TRY
BEGIN TRAN ins

    IF EXISTS(SELECT * FROM Test_Serializable ts WITH(xlock,ROWLOCK) WHERE ts.Id=1)
        RAISERROR(N'Row Exists',16,1);


    INSERT INTO Test_Serializable
    (
        Id,
        [Name]
    )
    VALUES
    (
        1,
        'nima'
    )
   COMMIT TRAN ins
     END TRY
     BEGIN CATCH
        DECLARE @a  NVARCHAR(1000);
        SET @a=ERROR_MESSAGE();
        ROLLBACK TRAN ins
        RAISERROR(@a,16,1);
     END CATCH

this script works fine but there is interesting point.

I run this script from 2 SSMS and step by step run this 2 scripts(in debug mode).Interesting point is however my table has no row but one of the script when reach IF EXIST statement lock the table.

My question is whether (XLOCK,ROWLOCK) locks entire table because there is no row?or it locks phantom row 🙂 !!???

Edit 1)

This is my scenario:

I have a table with for example 6 fields

this is Uniqueness Rules:

1)City_Code + F1_Code are Unique

2)City_Code + F2_Code are Unique

3)City_Code + F3_Code + F4_Code are uinque

the problem is user may want to fill city_code and F1_Code and when it want Insert it in other fileds we must have Empty String or 0 (for numeric fields) value.

If user want to fill City_Code + F3_Code + F4_Code then F1_Code and F2_Code must have Empty String values

How I can check this better?I can’t create any Unique Index for every rules

Answer 1

To answer your question, the SERIALIZABLE isolation level performs range locks which would include non-existant rows within the range.

http://msdn.microsoft.com/en-us/library/ms191272.aspx

Key-range locking ensures that the following operations are
serializable:

Range scan query

Singleton fetch of nonexistent row

Delete operation

Insert operation