关于一个表连接查询

SQL code

假如我有5条数据,1111222233334444其tabel 是usnitem 用select * From usnitem where usn in('1111','2222','3333','4444') and unp='00E'其结果是:usn                   csn                              upn                                                          --------------------- -------- -------------------------------1111                5555                            00E2222                6666                            00E3333                7777                            00E4444                8888                            00E在用select * From usnitem where usn in('5555','6666','7777','8888') and unp='00C'其结果：usn                   csn                              upn                                                          --------------------- -------- -------------------------------5555                AAAA                            00C6666                BBBB                             00C7777                CCCC                            00C8888                DDDD                           00C怎样一次性查出结果为：usn                   csn                              csn                                                          --------------------- -------- -------------------------------1111               5555                            AAAA2222               6666                            BBBB3333               7777                            CCCC4444               8888                            DDDD

SQL code

select usnitem.usn, usnitem.csn, b.csn From usnitem a, usnitem b  where a.usn in('1111','2222','3333','4444') and a.unp='00E'    and a.csn = b.usn and b.unp='00C';