shell 与sql如何混合使用？

danbaoyu

sql能否直接使用shell脚？
比如：
while read a
do

if [ a -le 4]
then
sqlplus sys/oracle@wyln as sysdba <<!
select a,b,c from tables 1 into temp a;
unload to 1.txt select * from a
!
fi
if [ a -le 4]
then
sqlplus sys/oracle@wyln as sysdba <<!
select a,b,c from tables 1 into temp a;
unload to 1.txt select * from a
!
fi

if [ a -gt 4]
then
sqlplus sys/oracle@wyln as sysdba <<!
select a,b,c from tables2 into temp a;
unload to 1.txt select * from a
!
fi
if [ a -le 4]
then
sqlplus sys/oracle@wyln as sysdba <<!
select a,b,c from tables 1 into temp a;
unload to 2.txt select * from a
!
fi
cat 1.txt 2.txt>>3.txt
sqlplus sys/oracle@wyln as sysdba <<!
load from 3.txt insert into temp a;
!
done<sj.txt
以上功能要实现根据不同a的大小查询不同的表，并把数据插入到一张临时表中。但每次都要开关数据库，能不能只开一次数据库，就可执行完毕？