Dear Zeyad,

It depends whether you data is indexed. If it is then you can use simple random sampling by randomly selecting the indexes, e.g. by using a random number generator. If it isn't then you could use stratified or clustered sampling.

Thanks a lot dear Peter

Going along with Peter, if the data is not indexed then first index the data then use the associated technique in whatever software you are using to draw a random sample.

Thanks a lot Patricia