04PLSQL编程基础-1-数据类型和变量概论.ppt

Note: The LONG datatype is similar to VARCHAR2, except that the maximum length of a LONG value is 32,760 bytes. Therefore values longer than 32,760 bytes cannot be selected from a LONG database column into a LONG PL/SQL variable. Note: The LONG datatype is similar to VARCHAR2, except that the maximum length of a LONG value is 32,760 bytes. Therefore values longer than 32,760 bytes cannot be selected from a LONG database column into a LONG PL/SQL variable. Note: The LONG datatype is similar to VARCHAR2, except that the maximum length of a LONG value is 32,760 bytes. Therefore values longer than 32,760 bytes cannot be selected from a LONG database column into a LONG PL/SQL variable. Declaring Scalar Variables The variable declaration examples shown in the slide are defined as follows: Declared variable to store an employee job title. Declared variable to count the iterations of a loop and initialize the variable to 0. Declared variable to accumulate the total salary for a department and initialize the variable to 0. Declared variable to store the ship date of an order and initialize the variable to one week from today. Declared a constant variable for the tax rate, which never changes throughout the PL/SQL block. Declared flag to indicate whether a piece of data is valid or invalid and initialize the variable to TRUE. The %TYPE Attribute When you declare PL/SQL variables to hold column values, you must ensure that the variable is of the correct datatype and precision. If it is not, a PL/SQL error will occur during execution. Rather than hard coding the datatype and precision of a variable, you can use the %TYPE attribute to declare a variable according to another previously declared variable or database column. The %TYPE attribute is most often used when the value stored in the variable will be derived from a table in the database or if the variable is destined to be written out to it. To use the attribute in place of t