insert into aa(nickname)
select 't'
where not exists(select * from aa where ids=5)
当aa表中的ids列没有值为5的记录时,将字符串" 't' "插入aa 表的 nickname列中
insert into aa(col1,col2,col3,col4) select num1,'str2','str3',num4
where not exists(select * from aa where col_n=val_n)