PHP Mysqli Can i get corrupted data by simultaneously load

Question

i have a question, if 100 users load the page simultaneously and i have the script like this:

select(some data)
if(exist)
{ update the data / etc }

and another page script like this:

delete(the data above)

Can something like this happen?

select(some data)
if(exist) // we get that exist
{
   // and here the date will be deleted by page 2 and cannot update or will be corrupted data
}