Implementing SQL_VARIANT in a Memory-Optimized Table

 

Consider an example of a table with SQL_VARIANT column:

CREATE TABLE [dbo].[T1](  
  [Key] [sql_variant] NOT NULL  
)  

Assume that the key column can only be either a BIGINT or NVARCHAR(300). You can model this table as follows:

-- original disk-based table  
CREATE TABLE [dbo].[T1_disk](  
       [Key] int not null primary key,  
       [Value] [sql_variant]  
)  
go  
  
insert dbo.T1_disk values (1, 12345678)  
insert dbo.T1_disk values (2, N'my nvarchar')  
insert dbo.T1_disk values (3, NULL)  
go  
  
-- new memory-optimized table  
CREATE TABLE [dbo].[T1_inmem](  
       [Key] INT NOT NULL PRIMARY KEY NONCLUSTERED,  
       [Value_bi] BIGINT,  
       [Value_nv] NVARCHAR(300),  
       [Value_enum] TINYINT NOT NULL  
) WITH (MEMORY_OPTIMIZED=ON)  
go  
  
-- copy data   
INSERT INTO dbo.T1_inmem  
  SELECT [Key],  
              CASE WHEN SQL_VARIANT_PROPERTY([Value], 'basetype') = 'bigint' THEN convert (bigint, [Value])  
              ELSE NULL END,  
              CASE WHEN SQL_VARIANT_PROPERTY([Value], 'basetype') != 'bigint' THEN convert (nvarchar(300), [Value])  
              ELSE NULL END,  
              CASE WHEN SQL_VARIANT_PROPERTY([Value], 'basetype') = 'bigint' THEN 1  
              ELSE 0 END  
  FROM dbo.T1_disk  
GO  
  
-- select data, converting back to sql_variant [will not work inside native proc]  
select [Key],   
       case [Value_enum] when 1 then convert(sql_variant, [Value_bi])   
    else convert(sql_variant, [Value_nv])   
    end  
from dbo.T1_inmem  

Now you can load data into [T1_HK] from T1 by opening a cursor on T1:

DECLARE T1_rows_cursor CURSOR FOR    
select *  
FROM dbo.T1  
  
OPEN T1_rows_cursor     
  
-- declare 1 variable each for column in HK table  
  
Declare  
@Key_biBIGINT = 0,  
@Key_nvnvarchar(300)= ' ',  
@Key_enumsmallint,  
@Keysql_variant  
  
FETCH NEXT FROM T1_rows_cursor INTO @key  
  
WHILE @@FETCH_STATUS = 0     
BEGIN     
  
-- setting the input parameters for inserting into the memory-optimized table  
-- convert SQL Variant types  
-- @key_enum =1 represents BIGINT  
if (SQL_VARIANT_PROPERTY(@Key, 'basetype') = 'bigint')  
begin  
set @key_bi = convert (bigint, @Key)  
set @key_enum = 1  
set @key_nv = 'invalid'  
end  
else  
begin  
set @Key_nv = convert (nvarchar (300), @Key)  
set @Key_enum = 0  
set @Key_bi = -1  
end  
  
-- inserting the row  
INSERT INTO T1_HK VALUES (@Key_bi, @Key_nv, @Key_enum)  
  
FETCH NEXT FROM T1_rows_cursor INTO @key  
END  
  
CLOSE T1_rows_cursor     
DEALLOCATE T1_rows_cursor  

You can convert data back to SQL_VARIANT as follows:

case [Key_enum] when 1 then convert(sql_variant, [Key_bi])   
                       else convert(sql_variant, [Key_nv])   
                       end  

Migrating to In-Memory OLTP

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