查某一表的行数
select max(rownum) from tablename
插入数据之前判断是否重复
insert into tablename (coloum1,coloum2) select coloum1,coloum2 from dual where not exists( select 1 from tablename where coloum1 ="value1" and coloum2="value2";
查询时检索数据库中字段
select coloum1 , coloum1 ,coloum3 from table where instr(‘coloum1‘,查询字符)>0 or instr(‘coloum3‘,查询字符)>0 or instr(‘coloum3‘,查询字符)>0
去除表中有字段为空的数据
delete from table where coloum is null ;
原文：http://www.cnblogs.com/vitre/p/5101991.html