title: what are mysql sessions used in isolation level
body: <p>I am reading about isolation level in mysql database, while reading I came across the following syntax</p>
  
  <pre><code>SET [GLOBAL | SESSION] TRANSACTION
      transaction_characteristic [, transaction_characteristic] ...
  
  transaction_characteristic:
      ISOLATION LEVEL level
    | READ WRITE
    | READ ONLY
  
  level:
       REPEATABLE READ
     | READ COMMITTED
     | READ UNCOMMITTED
     | SERIALIZABLE 
  </code></pre>
  
  <p>reference : <a href="http://dev.mysql.com/doc/refman/5.7/en/set-transaction.html" rel="nofollow">http://dev.mysql.com/doc/refman/5.7/en/set-transaction.html</a></p>
  
  <p>My question is, in 1st line of syntax, <code>SET [GLOBAL | SESSION] TRANSACTION</code>, what is <code>GLOBAL</code> and <code>SESSION</code> keywords. Can anyone explain it with example ?</p>
  
  <p>Can we start Transaction in particular session(through PHP or any other language)? or they are managed by mysql only ?</p>