To delete all pingbacks in WordPress you can use the mysql query below.
DELETE FROM wp_comments WHERE comment_type = 'pingback';
Cleanup
How to TRIM a string in MSSQL
To TRIM a string in MSSQL you can use the following Userdefinedfunction Snippet.
Sample MSSQL
CREATE FUNCTION dbo.TRIM(@inputString VARCHAR(MAX)) RETURNS VARCHAR(MAX) BEGIN RETURN LTRIM(RTRIM(@inputString)) END