Syntax:
SET [GLOBAL | SESSION] TRANSACTION
    transaction_characteristic [, transaction_characteristic] ...

transaction_characteristic: {
    ISOLATION LEVEL level
  | access_mode
}

level: {
     REPEATABLE READ
   | READ COMMITTED
   | READ UNCOMMITTED
   | SERIALIZABLE
}

access_mode: {
     READ WRITE
   | READ ONLY
}

This statement specifies transaction characteristics. It takes a list
of one or more characteristic values separated by commas. Each
characteristic value sets the transaction isolation level or access
mode. The isolation level is used for operations on InnoDB tables. The
access mode specifies whether transactions operate in read/write or
read-only mode.

In addition, SET TRANSACTION can include an optional GLOBAL or SESSION
keyword to indicate the scope of the statement.

URL: https://dev.mysql.com/doc/refman/5.7/en/set-transaction.html

