邹老大的代码的疑问
以下是邹老大的关于查询阻塞进程信息的代码：

-- ===========================================
-- 获取阻塞的 session_id 及阻塞时间
DECLARE @tb_block TABLE(
top_blocking_session_id smallint,
session_id smallint,
blocking_session_id smallint,
wait_time int,
Level int,
blocking_path varchar(8000),
PRIMARY KEY(
session_id, blocking_session_id)
)
INSERT @tb_block(
session_id,
blocking_session_id,
wait_time)
SELECT
session_id,
blocking_session_id,
wait_time = MAX(wait_time)
FROM sys.dm_exec_requests
WHERE blocking_session_id > 0
GROUP BY session_id, blocking_session_id

-- ===========================================
-- 处理阻塞的 session_id 之间的关系
DECLARE
@Level int
SET @Level = 1

INSERT @tb_block(
session_id, top_blocking_session_id, blocking_session_id,
Level, blocking_path)
SELECT DISTINCT
blocking_session_id, blocking_session_id, 0,
@Level, RIGHT(100000 + blocking_session_id, 5)
FROM @tb_block A
WHERE NOT EXISTS(
SELECT * FROM @tb_block
WHERE session_id = A.blocking_session_id)
WHILE @@ROWCOUNT > 0
BEGIN
SET @Level = @Level + 1
UPDATE A SET
top_blocking_session_id = B.top_blocking_session_id,
Level = @Level,
blocking_path = B.blocking_path 
+ RIGHT(100000 + A.session_id, 5)
FROM @tb_block A, @tb_block B
WHERE A.blocking_session_id = B.session_id
AND B.Level = @Level - 1
END

-- ===========================================
-- 如果只要显示阻塞时间超过多少毫秒的记录，可以在这里做一个过滤
-- 这里假设阻塞时间必须超过 1 秒钟(1000毫秒)
DELETE A 
FROM @tb_block A
WHERE NOT EXISTS(
SELECT * FROM @tb_block
WHERE top_blocking_session_id =A.top_blocking_session_id
AND wait_time >= 1000)

-- ===========================================
-- 使用 DBCC INPUTBUFFER 获取阻塞进程的 T-SQL 脚本
DECLARE @tb_block_sql TABLE(
id int IDENTITY,
EventType nvarchar(30),
Parameters int,
EventInfo nvarchar(4000),
session_id smallint)
DECLARE
@session_id smallint
DECLARE tb CURSOR LOCAL STATIC FORWARD_ONLY READ_ONLY
FOR
SELECT DISTINCT
session_id
FROM @tb_block
OPEN tb
FETCH tb INTO @session_id
WHILE @@FETCH_STATUS = 0
BEGIN
INSERT @tb_block_sql(
EventType, Parameters, EventInfo)
EXEC(N'DBCC INPUTBUFFER(' + @session_id + ') WITH NO_INFOMSGS')
IF @@ROWCOUNT > 0
UPDATE @tb_block_sql SET
session_id = @session_id
WHERE IDENTITYCOL = @@IDENTITY

FETCH tb INTO @session_id
END
CLOSE tb
DEALLOCATE tb

-- ===========================================
-- 显示阻塞进程信息
;WITH
BLK AS(
SELECT
A.top_blocking_session_id,
A.session_id,
A.blocking_session_id,
A.Level,
A.blocking_path,
SQL = B.EventInfo
FROM @tb_block A
LEFT JOIN @tb_block_sql B
ON A.session_id = B.session_id
)
SELECT
-- BlockPath = REPLICATE(' ', Level * 2 - 2)
-- + '|-- '
-- + RTRIM(session_id),
BLK.top_blocking_session_id,
BLK.session_id,
BLK.blocking_session_id,
BLK.Level,
wait_type = P.waittype,
wait_time = P.waittime,
last_wait_type = P.lastwaittype,
wait_resource = P.waitresource,
P.login_time,
P.last_batch,
P.open_tran,
P.status,
host_name = P.hostname,
P.program_name,
P.cmd,
login_name = P.loginame,
BLK.SQL,
current_sql = T.text,
current_run_sql = SUBSTRING(T.text,
P.stmt_start / 2 + 1,
CASE
WHEN P.stmt_end = -1 THEN LEN(T.text)
ELSE (P.stmt_end - P.stmt_start) / 2+1
END)
FROM BLK
-- 简省代码起见，直接引用 sysprocess, 读者可以改为引用前述介绍的“查询进程"的脚本进行替换
INNER JOIN