isql: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/isql - from package: unixODBC

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/isql - from package: unixODBC

You may install the required package with command apt-get install {package}

Error in other languages:
isql: bevel nie gevind nie
isql: comandă negăsită
isql: comando não encontrado
isql: commande introuvable
isql: command not found
isql: käsku ei ole
isql: không tìm thấy lệnh
isql: komanda nerasta
isql: Kommando nicht gefunden.
isql: kommandot finns inte
isql: komut yok
isql: nie znaleziono polecenia
isql: níor aimsíodh an t-ordú
isql: no se encontró la orden
isql: no s'ha trobat l'ordre
isql: opdracht niet gevonden
isql: parancs nem található
isql: perintah tidak ditemukan
isql: príkaz nenájdený
isql: příkaz nenalezen
isql: команда не найдена
isql: командата не е открита
isql: 命令找不到
isql: コマンドが見つかりません