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When constraints are created, they can be created either as deferrable or not deferrable. A constraint that is not deferred is checked immediately upon execution of each statement and if the constraint is violated, it is immediately rolled back. A constraint that is deferred will not be checked until a commit statement is issued. This is useful when inserting rows or updating values that reference other values that do not exist but are part of the overall batch of statements. By deferring the constraint checking until the commit is issued, we can complete the entire batch of entries before determining if there are any constraint violations.
Throughout this chapter, we've seen the results of many SQL queries. In some, we added functions like substr to reduce the size of the columns and keep the results confined within one line. In SQL*Plus, there are many parameters that can be set to control how the output is displayed. A list of all of the available settings is easily obtained by issuing the show all command within SQL*Plus. Alternatively, if you know the parameter and want to see its current value, the command show parameter_name will give you the answer. Before we close out this chapter, let's visit a number of the more useful SQL*Plus parameters.
The set linesize command tells Oracle how wide the line output is before wrapping the results to the next line. To set the line size to 100, enter the command set linesize 100. There is no semicolon required to end set commands.
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