sql - How can I increase the port value when I get "already allocated port number" -

in script set unique constraint port field. if once enter assigned port number new row value not insert. want increase port number when enter assigned port number. please me

#!/bin/bash  echo " --- enter database name ---" #name of database read databasename  echo " --- enter table name --- " #name of table read table_name  sqlite3 $databasename.db $table_name;  sqlite3 $databasename.db  "create table if not exists $table_name(cus_id integer primary key autoincrement unique,cus_name text not null unique ,cus_domain text unique,created_on default current_date,cus_status text not null,port integer not null unique);" #table creation  sqlite3 $databasename.db "select * $table_name;"  echo " --- enter total number of customer records want ---" read cus_count # number of rows value  echo "enter following details 1 one"  red='\033[0;31m' nc='\033[0m'  echo "---enter initial port number---" echo "!!!before enter port number please verify table!!!" read port  port_num=$port declare -a customer  for((i=1;i<=cus_count;i++)) echo "enter $i customer details"  echo "---enter customer name---" read c_name  d_name=${c_name,,} #echo $d_name  customer=$(sqlite3 $databasename.db "select cus_domain $table_name cus_domain '$d_name';")  cus in "${customer[@]}"  if [[ $d_name != $customer ]];      echo "---enter status(active/inactive)---"      read c_status    #sqlite3 $databasename.db "create unique index on $table_name(port) cus_status = 'active';"  if [[ "$port_num" == "$port_num" ]];        port_num=$(($port_num + 1))  c_domain="$c_name"     sqlite3 $databasename.db "insert or ignore $table_name (cus_name,cus_domain,cus_status, port) values(\"$c_name\",\"${c_domain,,}\",\"$c_status\",\"$port_num\") ;"  fi   else     echo -e "${red}!!!oops entered customer name  domain name assigned!!!${nc}"     echo -e "${red}please enter new customer name${nc}"  i=$(($i - 1))  fi done done  echo " --- records $table_name ---"  sqlite3 $databasename.db "select * $table_name;" 

for example table has following values:

1|ajax|ajax|2017-08-21|active|8062  2|vvcoe|vvcoe|2017-08-21|active|8063 

now enter new row values insert

3|vvm|vvm|2017-08-21|active|8063 

here 8063 assigned port number

so want increase port value 8064.

how can modify this..?