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CHECK Constraints in SQL
A CHECK constraint is a table constraint defined using the key word CHECK, as already illustrated in several examples in this chapter. In particular, a CHECK constraint can be used to express a constraint such as the one shown in Example, referred to in the theory book as a tuple constraint (so one might call it a row constraint in SQL). This is clearly the way most SQL users would prefer to express such a constraint.
Parameter and Keyword Description: cursor_name: This identifies an explicit cursor formerly declared within the present scope. cursor_variable_name: These identif
Control Structures The Control structures are the most important PL/SQL extension to the SQL. Not only does PL/SQL let you manipulate Oracle data, it lets you process the data
Overriding Default Locking By default, the Oracle locks the data structures for you automatically. Though, you can request exact data locks on rows or tables when it is to you
Operator Precedence The operations within an expression are completed in a particular order depending on their precedence (priority). The table shows the default order of the op
Comparison Operators The Comparison operators can compare one expression to another. The outcome is always true, false, or null. Usually, you use a comparison operators in condi
Updating Objects: To change the attributes of objects in an object table, you can use the UPDATE statement, as the illustration below shows: BEGIN UPDATE persons p SET p
Functions The function is a subprogram which can take parameters and be invoked. Normally, you can use a function to calculate a value. The function has 2 sections: the specifi
Redeclaring Predefined Exceptions Keep in mind that, the PL/SQL declares predefined exceptions globally in the package STANDARD; Therefore you need not declare them yourself.
Autonomous versus Nested Transactions Though an autonomous transaction is started by the other transaction, it is not a nested transaction for the reasons shown below: (i)
Cursor Variables Similar to a cursor, cursor variable points to the current row in the result set of a multi-row query. But, dissimilar a cursor, a cursor variable can be opene
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