数据库查询问题

[ql_nanjing]

高手们，条件查询如下：
select * from table1 where table1.字段A = some(查询语句2)
当“查询语句2”结果不为空时，按照满足的条件进行查询；当“查询语句2”结果为空时，忽略查询条件，直接执行“select * from table1”,请问这个查询该怎么写？

[chengccy]

有点奇怪的需求, 改成exists , 判断2次: select * from table1 where exists (select 1 from table2 where table2.字段a=table1.字段a union all select 1 from dual where (select count(1) from table2)=0); 例子:

WITH TMP AS
 (SELECT LEVEL AS L FROM DUAL CONNECT BY LEVEL < 10) 
SELECT *
FROM   TMP T
WHERE  EXISTS (SELECT L
        FROM   TMP
        WHERE  MOD(L, 2) = 3
        AND    L = T.L
        UNION ALL
        SELECT 1
        FROM   DUAL
        WHERE  (SELECT COUNT(1) FROM TMP WHERE MOD(L, 2) = 3) = 0)

[ql_nanjing]

谢谢，搞定！