How to embed sql query into our shell script?

Shell Programming and Scripting
1

Hi I would like to embed a sql query in my shell script.
Also, before any the sql query is executed, i would like to validate username and password.

2 
sqlplus -s $user/$passwrd <<ENDOFSQL
whenever sqlerror exit sql.sqlcode;
select sysdate from dual;
exit;
ENDOFSQL

RetCode=$?

#Check the return code from SQL Plus
if [ $RetCode != 0 ]
then
  echo "********************"
  echo "ERROR: The SQL Plus Command Failed. RetCode: $RetCode"
else
  echo "********************"
  echo "SQL Plus Successfully Ran. RetCode: $RetCode"
fi

If provided userid and password is not correct , then sql query will not execute and script will exit, so no need to validate userid and password here.