SQL Server Bitwise Processing like C# Enum Flags

Question

How can one use in SQL Server the processing of the Flags such as on enums in C#?

---

For example, how would one return a list of users that are part of a list or conditions like so:

ConditionAlpha = 2
ConditionBeta  = 4
ConditionGamma = 8

...

Then there will be users with some of these conditions against them like so:

User1: 6 (conditions Alpha and Beta)
User2: 4 (condition Beta)
User3: 14 (conditions Alpha, Beta and Gamma)

...

We want to be able to do a query where we say get all users with the first condition Alpha and in this scenario it would return users 1 and 3 even though they have other conditions as well.

Answer 1

The bitwise operator for checking whether a flag is set in SQL is &. The WHERE clause needs to evaluate to a BOOLEAN expression, like this:

create table #temp (id int, username varchar(20), flags int)

insert into #temp values
(1, 'User1', 6 /* (2 | 4) */),
(2, 'User2', 4),
(3, 'User3', 14 /* (2 | 4 | 8) */)

declare @ConditionOne int = 2

select *
from   #temp
where  flags & @ConditionOne <> 0

declare @ConditionTwo int = 4

select *
from   #temp
where  flags & @ConditionTwo <> 0

declare @ConditionThree int = 8

select *
from   #temp
where  flags & @ConditionThree <> 0

drop table #temp

These queries return the following resultsets:

id          username             flags
----------- -------------------- -----------
1           User1                6
3           User3                14

id          username             flags
----------- -------------------- -----------
1           User1                6
2           User2                4
3           User3                14

id          username             flags
----------- -------------------- -----------
3           User3                14

Answer 2

While the bitwise operator suggested by James will work, it will not be very performant in a relational database, especially when you try to scale to millions of records. The reason is that functions in the where clause are not sargable (they prevent an index seek).

What I would do would be create a table which contains all possible combinations of flags and conditions, which will enable an index seek on the condition.

Populate FlagConditions. I used a single (tinyint). Should you need more Flags, you should be able to expand on this approach:

CREATE TABLE FlagConditions (
      Flag TINYINT
    , Condition TINYINT
    , CONSTRAINT Flag_Condition PRIMARY KEY CLUSTERED (Condition,Flag)
);

CREATE TABLE #Flags (
      Flag TINYINT IDENTITY(0,1) PRIMARY KEY CLUSTERED
    , DummyColumn BIT NULL);
GO

INSERT #Flags
        ( DummyColumn )
SELECT NULL;
GO 256

CREATE TABLE #Conditions(Condition TINYINT PRIMARY KEY CLUSTERED);

INSERT #Conditions ( Condition )
    VALUES  (1),(2),(4),(8),(16),(32),(64),(128);

INSERT FlagConditions ( Flag, Condition )        
    SELECT
    Flag, Flag & Condition
    FROM #Flags f
    CROSS JOIN #Conditions c
    WHERE Flag & Condition <> 0;

DROP TABLE #Flags;
DROP TABLE #Conditions;

Now you can use the FlagConditions table any time you need to efficiently seek on an enum bitwise condition:

DECLARE @UserFlags TABLE (Username varchar(10), Flag tinyint);

INSERT @UserFlags(Username, Flag)
    VALUES ('User1',6),('User2',4),('User3',14);

DECLARE @Condition TINYINT = 2;

SELECT u.*
FROM @UserFlags u
INNER JOIN FlagConditions fc ON u.Flag = fc.Flag
WHERE fc.Condition = @Condition;

This returns:

Username   Flag
---------- ----
User1      6
User3      14

Your DBA will thank you for going this set oriented route.

Answer 3

I had almost the same problem and could come up with such solution:

SELECT  t.value
    , ISNULL(t.C1 + ', ', '') + ISNULL(t.C2, '') + ISNULL(', ' + t.C3, '') AS [type]
FROM
(
    SELECT value,
        CASE WHEN (type & 2) <> 0  THEN 'Type1' END AS C1,
         CASE WHEN (type & 4) <> 0  THEN 'Type2' END AS C2,
         CASE WHEN (type & 8) <> 0  THEN 'Type3' END AS C3
    FROM db.Agent
) t

and the result was as follows:

value       type
----------  ------------------------------------
14          Type1, Type2, Type3
12          Type2, Type3
14          Type1, Type2, Type3

Answer 4

C# Enum: CopEntry = 1 << 17

SQL Server: case when (Features & power(2, 17)) = 0 then 0 else 1 end as COPEntry

Answer 5

Same as except it's pure T-SQL so it works not only in SSMS or elsewhere

DROP TABLE IF EXISTS flag_conditions
CREATE TABLE flag_conditions
(
    flag      TINYINT,
    condition TINYINT,
    CONSTRAINT Flag_Condition PRIMARY KEY CLUSTERED (condition, flag)
);

CREATE TABLE #Flags
(
    Flag        TINYINT IDENTITY (0,1) PRIMARY KEY CLUSTERED,
    DummyColumn BIT NULL
);
GO

WITH x AS (SELECT n FROM (VALUES (0), (1), (2), (3), (4), (5), (6), (7), (8), (9)) v(n))
INSERT #Flags
    (DummyColumn)
SELECT NULL
FROM (
         SELECT ROW_NUMBER() OVER (ORDER BY (SELECT NULL)) AS n
         FROM x ones,
              x tens,
              x hundreds,
              x thousands
     ) t
WHERE n <= 256;

SELECT *
FROM #Flags;

CREATE TABLE #Conditions
(
    Condition TINYINT PRIMARY KEY CLUSTERED
);

INSERT #Conditions (Condition)
VALUES (1),
       (2),
       (4),
       (8),
       (16),
       (32),
       (64),
       (128);

INSERT flag_conditions (flag, condition)
SELECT Flag,
       Flag & Condition
FROM #Flags f
         CROSS JOIN #Conditions c
WHERE Flag & Condition <> 0;

DROP TABLE #Flags;
DROP TABLE #Conditions;

SELECT *
FROM flag_conditions;