SQL语句，稍微有些难度。

[no_com]

SQL语句，稍微有些难度。
表：A
TID NUM
1 11
2 22
3 33
4 44
===============
经过查询后形成如下格式：
TID NUM PNUM PPNUM
a xx xx xx
===============
注：NUM用a取得的NUM（SELECT NUM FROM A WHERE A.TID=a）;
PNUM 用a-1取得的NUM（SELECT NUM FROM A WHERE A.TID=a-1）;
PPNUM用a-2取得的NUM（SELECT NUM FROM A WHERE A.TID=a-2）;

怎么写SQL语句？

[victorycyz]

你不是已经写出来了吗。

[zsgzsgzsg]

SELECT A.NUM, A_1.NUM AS PNUM, A_2.NUM AS PPNUM
FROM (A LEFT JOIN A AS A_1 ON A.TID = A_1.TID+1) LEFT JOIN A AS A_2 ON A_1.TID = A_2.TID+1
WHERE A.TID= a

[no_com]

我想通过一条语句写出sql语句

[GhSoft]

select A.tid, A.Num as num, B.Num as pnum, C.Num as ppnum
from A A, A B ,A C
where A.Tid = a and
B.tid = a-1 and
C.tid = a-2

[ZJYUNCSUNDN]

SELECT TID,(SELECT NUM FROM A WHERE A.TID=a) AS NUM ,（SELECT NUM FROM A WHERE A.TID=a-1 ) AS PNUM,（SELECT NUM FROM A WHERE A.TID=a-2）AS PPNUM FROM A WHERE TID=A AND TID=A-1 AND TID=A-2