The following program defines a variable and assigns it a value: -- This is found in substitution. Date, numeric, and string literals are covered in Chapter 3. The default file extension is. This means you can call a filename without its. The following demonstrates calling the substitution.
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The line starting with old designates where your program accepts a substitution, and new designates the run-time substitution. Assigning a string literal that is too large for the variable fires an exception. Exception blocks manage raised errors. A generic exception handler manages any raised error. The following exception. Assigning the variable raises an exception.
The outermost programming block controls the total program flow, while nested programming blocks control their subordinate programming flow. Each anonymous- or named-block programming unit can contain an exception section. Error are raised and put in a first-in, last-out queue, which is also known as a stack.
Scalar variables hold only one thing, while composite variables hold more than one thing. The preceding programs have demonstrated how you declare and assign values to scalar variables.
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Variables have local scope only. The exceptions to that rule are nested anonymous blocks. Nested anonymous blocks operate inside the defining block. They can thereby access variables from the containing block. A declaration of a number variable without an explicit assignment makes its initial value null. You can use the default value or assign a new value in the execution block.
Both are demonstrated next. They typically assign a value to a variable on the left.
The right operand can be a value, variable, or function. Functions in this context are also known as expressions. Oracle 11g performs many implicit casting operations. They fail to follow the common rule of programming: implicitly cast when there is no loss of precision. This means you can assign a complex number like 4. Likewise, there are a series of functions to let you explicitly cast when there is greater risk of losing precision. You should choose carefully when you explicitly downcast variables.
Appendix J covers explicit casting functions. There are also several product-specific datatypes. They support various component products in Oracle 11g. Chapter 3 covers all the comparison, concatenation, logical, and mathematical operators. You have now reviewed variables, assignments, and operators.
They check a logical condition and branch program execution, or they iterate over a condition until it is met or they are instructed to exit. The conditional structures section covers if, elsif, else, and case statements.
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Conditional Structures Conditional statements check whether a value meets a condition before taking action. The IF statement that has two subtypes, if-then-else and if-then-elsif-then-else. This is another legacy from Pascal and ADA. Boolean outcomes then apply to the combination of expressions. You can negate single or combined outcomes with the NOT operator. Logical operators support conjoining and including operations. A conjoining operator, AND, means that both statements must evaluate as true or false.
An include operator, OR, means that one or the other must be true.
Include operators stop processing when one statement evaluates as true. Conjoining operators check that all statements evaluate as true. Other operands can be any valid datatype that works with the appropriate comparison operator, but remember variables must be initialized. Problems occur when you fail to initialize or handle non-initialized variables in statements.
It lets you substitute a value for any null value variables. The NVL function takes two parameters: the first is a variable, and the second is a literal, which can be a numeric, string, or constant value. The two parameters must share the same datatype. The single quote mark is a reserved character for delimiting strings.
You backquote an apostrophe by using another apostrophe, or a single quote, inside a delimited string. You can also substitute another backquoting character, as covered in the Oracle 10g recent features section. The if-then-elsif-then-else statement works like the if-then-else statement but lets you perform multiple conditional evaluations in the same IF statement. A CASE statement works like the if-then- elsif-then-else process. A simple CASE statement takes a scalar variable as an expression and then evaluates it against a list of like scalar results.
Putting it in adds clarity. The program evaluates WHEN clause results as expressions, finding that 3 is less than 5. It then prints Three is less than five. It has also suggested an alternative to non-initialized variables.
source site Loops typically work in conjunction with cursors but can work to solve other problems, like searching or managing Oracle collections. FOR loops manage how they begin and end implicitly.
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Numeric FOR loops take two implicit actions. They automatically declare and manager their own loop index, and they create and manage their exit from the loop. The loop index is the i variable, and the loop index scope is limited to the FOR loop. A function should only use the default IN type of parameter. The only out value from the function should be the value it returns. Procedures resemble functions in that they are named program units that can be invoked repeatedly. The primary difference is that functions can be used in a SQL statement whereas procedures cannot.
Another difference is that the procedure can return multiple values whereas a function should only return a single value. The procedure begins with a mandatory heading part to hold the procedure name and optionally the procedure parameter list. A simple procedure might look like this:. The standalone or package procedures, stored in the database, are referred to as " stored procedures ".