You can only execute SQL statements after opening a database session. To open a database session, log on to a database as a database user with user name and password, using either a database tool or an interface. When you open a database session, you can override some session properties, including the following:
Later, you terminate the database session with the corresponding command, or the database system terminates the database session when the time-out value is exceeded.
The database system assigns a user task to each database session. To configure the maximum number of user tasks, and thereby the maximum number of database sessions, use the MaxUserTasks general database parameter. When configuring these database parameters, bear in mind that database tools implicitly open and close database sessions for specific actions.
Database Studio, Logging on to a Database
Database Administration, General Database Parameters
SQLCLI, Logging on to a Database
Database Manager CLI, SQL Access to the Database Instance
SQL Reference Manual, CONNECT Statement