How To Update A BLOB In SQL SERVER Using TSQL

问题:

How do I update a BLOB field only using TSQL (for example from SSMS and not using any code such as ADO.Net or Linq)?

回答1:

There are two ways to SELECT a BLOB with TSQL:

SELECT * FROM OPENROWSET (BULK 'C:\Test\Test1.pdf', SINGLE_BLOB) a

As well as:

SELECT BulkColumn FROM OPENROWSET (BULK 'C:\Test\Test1.pdf', SINGLE_BLOB) a

Note the correlation name after the FROM clause, which is mandatory.

The second version can be used for a UPDATE as in the following example:

UPDATE MyTable 
SET blobField = 
   (SELECT BulkColumn FROM OPENROWSET (BULK 'C:\Test\Test1.pdf', SINGLE_BLOB) a) 
WHERE (CriteriaField = @criteria)

For partial updates one can use the SET .WRITE mutator as described in this MSDN article, here is the syntax:

UPDATE MyTable SET BlobField .WRITE (expression, @offset, @length) WHERE (CriteriaField = @criteria)

Note that the WRITE mutator can only be used on NON-NULL fields.

In fact this can also be used to do a full update (if the column does not contain NULL), by setting @offset to 0 and @length to NULL (or to the actual length), as in the following example:

DECLARE @tmp VARBINARY(MAX) --Change to the correct datatype here
SELECT @tmp = BulkColumn FROM OPENROWSET (BULK 'C:\Test\Test1.pdf', SINGLE_BLOB) a
UPDATE MyTable SET BlobField .WRITE (@tmp, 0, NULL) WHERE (CriteriaField = @criteria)