Oracle XSQL- P13 pps

Table 8.106 Simple Conversion Functions FUNCTION DESCRIPTION Asciistr Returns the ASCII string. Non-ASCII characters are converted to their Unicode (UTF-16) binary code value. Chartorowid Changes a string to a row id. Compose Returns a fully normalized Unicode string. Hextoraw Converts a hexadecimal number to a raw value. Rawtohex Converts a raw value to a hexadecimal number. Rowidtochar Converts a row id to a string. To_char Converts argument to a string. To_clob Converts argument to a CLOB. To_date Converts argument to a date. To_dsinterval Converts argument to a day-second interval. To_lob Converts argument to a LOB. To_multi_byte Converts a single character to a multibyte character. To_nchar Identical to to_char, except that it converts to the national character set. To_nclob Converts to the national character set. To_number Converts string to number. Generally not used, because Oracle automatically performs the conversion. To_singlebyte Converts a multibyte character to single byte if possible. To_yminterval Converts argument to a year-month interval. When used with dates, the to_char function takes the same format as that described in the “Date Formatting” section. When the to_char function is passed a number, it must decide how to appropriately output the string. It does this by using a format mask similar to the date format mask you learned about earlier. The most important element is the number 9. It represents a significant digit, and the number of 9’s repre- sents the number of significant digits that you want displayed. Table 8.107 lists the number-format elements. 220 Chapter 8 Table 8.107 Number-Format Elements ELEMENT DESCRIPTION A significant digit A padding zero. Usually appears on the left. $ Places a dollar sign in the output. , Places a comma in the output. . Places a period in the output. B Zero values are displayed as blanks. MI Negative sign for negative values. S Forces the sign of the number to be displayed. PR Places negative values to be displayed in angle brackets. D TDecimal point. G Group separator. C The International Organization for Standardization (ISO) currency indicator. L Local currency indicator. V Scaled values. RN Displays value in Roman numerals. Convert The convert function converts one character set to another. If a character doesn’t exist in the destination character set, a replacement character appears. SELECT CONVERT(‘Ä Ê Í Õ Ø A B C D E ‘, ‘US7ASCII’, ‘WE8ISO8859P1’) AS convert_str FROM DUAL Oracle SQL 221 Table 8.108 lists the results. Table 8.108 Convert Results CONVERT_STR A E I ? ? A B C D E ? Decompose The decompose function returns a Unicode string after decomposition. SELECT decompose(‘Châteaux’) AS decompose_str FROM dual Table 8.109 lists the results: Table 8.109 Decompose Results DECOMPOSE_STR Châteaux Translate The translate function translates strings to either the database character set or the national character set. SELECT translate(‘text’ USING char_cs) AS str FROM dual Table 8.110 lists the results. Table 8.110 Translate Results STR text Unistr The unistr function returns a string in the database Unicode character set. SELECT UNISTR(‘\00D6’) AS str FROM dual 222 Chapter 8 Table 8.111 lists the results. Table 8.111 Unistr Results STR Ö Miscellaneous Functions The remaining functions don’t fit easily into the other categories. The most important functions to the XSQL developer are decode, which allows you to write conditional logic into your SQL functions, and nvl, which allows you to substitute a value when NULL is encountered. Table 8.112 lists the functions. Table 8.112 Miscelleneous Functions NAME DESCRIPTION Bfilename Returns a bfilename based on a specified directory. Coalesce Returns the first nonnull expression in list of arguments, which are expressions. Decode Compares an expression to any number of search values that are mated to results. The result is returned for the first search value to match. If none match, a default value will be returned. Dump Returns a dump of internal information for the given expression. Empty_blob Returns an empty BLOB. Empty_clob Returns an empty CLOB. Nls_charset_decl_len Returns the declaration width of an NCHAR column. Nls_charset_id Returns a character set id number for a character name. Nls_charset_name Returns a character set name for a character set id. Nullif Returns null if two expressions are equal, the first expression otherwise. Nvl If an argument is null, replace it with the given value. (continues) Oracle SQL 223 Table 8.112 Miscelleneous Functions (Continued) NAME DESCRIPTION Nvl2 If the first expression isn’t null, return the second. If the first expression is null, return the third. Sys_guid Returns a system global unique identifier. Uid Returns the user id of the user who logged on. User Returns the user name of the user who logged on. Vsize Returns the number of bytes in the internal representation of the given expression. Moving On In the previous chapters, you saw examples of some SQL in the code. This chapter helped to fill out your understanding and showed you the ins and outs of SQL. The next three chapters delve more deeply into the Oracle database technologies. The tech- nologies described are by no means an inclusive representation of the entire Oracle database; rather, they are the technologies that you’ll find most useful in conjunction with XSQL. 224 Chapter 8 225 CHAPTER 9 PL/SQL stands for the procedural language extensions to SQL. It gives you a new level of power when working with the database. Instead of being limited to the functions pro- vided by SQL, you can write your own. You can also use all of the basics of procedural programming: loops, conditional statements, variables, and encapsulation. The PL/SQL code that you will be creating here is stored in the database. Unlike code that executes at the client, server-side PL/SQL doesn’t incur the costs of network roundtrips. Calls to PL/SQL can be integrated closely with SQL. Likewise, PL/SQL can be used from XSQL and can be a valuable tool for you as you develop your XSQL applications. This section outlines how to create PL/SQL code and the different options that are available. Hello, PL/SQL! Your first step is to create a simple PL/SQL function and execute it from an XSQL page. Your function will simply return the string “Hello, PL/SQL!” when called. As with all PL/SQL code, you should create it in its own file and then load the file using SQL*PLUS. By doing it this way, if you need to change the code later, it will be easy to do so. PL/SQL TIP If you get a message that you have received compilation errors, you can use the SHOW ERRORS command from SQL*PLUS to see what those errors are. For this example, you’ll create a package. A package is a set of functions, parameters, and variables. The definition looks a bit like a class, but PL/SQL isn’t an object- oriented language. Rather, the PL/SQL package is just an encapsulation mechanism. For this example, our package contains just one sub-routine. Your subroutines can be stand-alone, but your code will be better organized and more reusable if you always use packages. CREATE OR REPLACE PACKAGE hello_pkg AS FUNCTION hello_plsql (param NUMBER) RETURN VARCHAR2; END hello_pkg; Your next step is to create the body of your package. This includes the actual code of your hello_plsql. As is befitting a first try, our code is simple. It takes the param, assumes that it is the empno for a row in the emp table, looks up the salary, and appends it to the string “hello pl/sql:.” If the parameter passed doesn’t match an empno in the database, then the string “invalid param” is returned. CREATE OR REPLACE PACKAGE BODY hello_pkg AS package body header FUNCTION hello_plsql (param NUMBER) function header RETURN VARCHAR2 IS hello_str VARCHAR2(20); sal_val NUMBER(7,2); declaration block BEGIN hello_str:=’hello pl/sql ‘; set the string SELECT sal INTO sal_val SELECT statement. FROM emp INTO is used to set WHERE param=empno; the sal_val variable IF sal_val=NULL THEN conditional statement. sal_val:=-1; END IF; hello_str:=hello_str || sal_val; combining the strings RETURN hello_str; EXCEPTION if the SELECT statement WHEN NO_DATA_FOUND THEN returned nothing, RETURN ‘invalid param’; this code executes. END; END hello_pkg With this package successfully compiled, you can invoke the function just like you invoked a lot of the SQL functions. Just select it as a pseudocolumn from the dual table. Just pass to it an employee ID that you know is valid, such as 7900. SELECT hello_pkg.hello_plsql(7900) AS hello_plsql FROM dual You should get the following result: hello pl/sql 950 226 Chapter 9 Of course, you aren’t limited to only using this function with the dual table. You can use this function anywhere that functions are permitted. In this example, the function is called as an element in the SELECT statement of the emp table. SELECT hello_pkg.hello_plsql(empno) AS hello_plsql FROM emp WHERE deptno=10 In this case, the function is called for each row in emp where deptno is equal to ten. The result of this statement should look like this: hello pl/sql 2450 hello pl/sql 5000 hello pl/sql 1300 Your final step is to use this example in an XSQL page. Your XML page will look like this: <?xml version=”1.0”?> <page connection=”demo” xmlns:xsql=”urn:oracle-xsql”> <xsql:query> SELECT hello_pkg.hello_plsql(empno) AS hello_plsql FROM emp WHERE deptno=10 </xsql:query> </page> This should produce output as seen in Figure 9.1. Figure 9.1 XSQL and the hello_plsql function. PL/SQL 227 Structure The preceding example gave you a taste of PL/SQL code. Now you will step back and look at how PL/SQL is structured. Because you created a named function inside of a package in the first example, you have already seen most of the structural components that PL/SQL code can have. In these pages, you’ll learn the names for the parts that you have already learned and see what the other pieces are. PL/SQL code is defined as blocks. The individual statements (such as control state- ments, SQL statements, variable declarations, and variable assignments) are included in these blocks. Block header. This block formally names and contains another block. In our hello_plsql function, the line beginning with FUNCTION hello_plsql and ending in a semicolon was a block header. It contained a declaration block and an execution block. Likewise, the package declaration is another block header that contains all of the blocks in our sample code. Block headers are optional. If there is a block header, the code that it contains is a named block; in the absence of a block header, the code is an anonymous block. Named blocks are generally preferable because they are easier to reuse. Declaration section. The declaration section declares the variables that you want to use. It is also optional—there are many times that you don’t need to declare variables. Our hello_plsql function had a declaration block consisting of one line: sal_val NUMBER(7,2);. Any variable used in the execution section must be declared in the declaration section. Execution section. The execution section is the meat of your code. All of the code between the BEGIN statement and the EXCEPTION statement belongs to the exe- cution block. Exception section. The exception block handles errors that are encountered in the execution block. In the case of hello_plsql, it handles the case where the SELECT statement returns no rows. These blocks represent the core basics of PL/SQL code. In addition to these blocks, you can also have a package specification, which was the first statement that you exe- cuted. It declares the package to the world and declares what is in it. Now that you know the basic parts of PL/SQL, you can start examining each part in turn. Declaring Variables As described earlier, all of your variables must be declared in the declaration section. (This differs from C++ and Java, in which you can declare variables anywhere in your code.) There are many types of variables that can be declared. Many are simple scalar data types that are identical to what you have seen in SQL. You’ll learn those first. You can also have record variables that are data structures containing several different 228 Chapter 9 variables of possibly different types. As you would expect from any decent program- ming language, PL/SQL has arrays. Perhaps most important, PL/SQL has cursors. A cursor contains the results of a SQL SELECT statement. By using a cursor, your SQL code can easily iterate over data in your database. Scalar Variable Declarations Scalar variable declarations take the following form: name [CONSTANT] type [NOT NULL] [:=|DEFAULT initial_value] Using the CONSTANT keyword declares that the variable is a constant—the value can’t be changed. NOT NULL declares that the variable can never be set to a NULL value. Both of these keywords require that the initial value be set—either the assignment operator or the DEFAULT keyword can be used. Of course, you don’t have to declare a variable to be NOT NULL or CONSTANT if you simply want to set an initial value, and you aren’t required to set an initial value at all. You’ve already seen the easiest way to declare a variable in the hello_plsql example. In that code, you declared a scalar variable of type NUMBER(7,2) with the following line: sal_val NUMBER(7,2); This is the simplest scalar variable declaration. You give the variable name followed by the type. Perhaps more useful, though, is referencing an existing database column: sal_val emp.empno%TYPE; This declaration tells PL/SQL that you want the variable to take the type of the empno column in the emp table. If you know that you are going to be using the variable to set data from a specific column (as you did in our example), you should do it this way. First, if the underlying table changes, you don’t have to modify your code. Sec- ond, it becomes obvious to anyone reading your code that the variable is related to that particular column. The following lines show examples of all of the remaining permutations of declar- ing scalar variables: dummy_1 emp.empno%TYPE :=7900; dummy_2 NUMBER(7,2) :=7900; dummy_3 emp.empno%TYPE NOT NULL :=7900; dummy_4 NUMBER(7,2) NOT NULL :=7900; dummy_5 CONSTANT emp.empno%TYPE :=7900; dummy_6 CONSTANT NUMBER(7,2) :=7900; Though you should declare variables based on a database column whenever practi- cal, there are many cases in which this isn’t done. The following tables list all of the data types that you can use when you are explicitly declaring the types of your variables. PL/SQL 229 [...]... Equivalent to INTEGER NATURAL BINARY INTEGER BINARY INTEGER restricted to nonnegative values but can be NULL NATURALN BINARY INTEGER BINARY INTEGER restricted to nonnegative and can’t be NULL The internal Oracle NUMBER data type NUMBER NUMERIC NUMBER Synonym for NUMBER Stores signed integers between -2,147,483,647 and 2,147,483,647 Faster than NUMBER PLS_INTEGER POSITIVE BINARY INTEGER BINARY INTEGER restricted... and the instantiation of an actual index: TYPE ibt_emp_type IS TABLE OF emp%rowtype INDEX BY BINARY INTEGER; emp_idx ibt_emp_type; WARNING The VARCHAR2 option of the INDEX BY clause is only available in Oracle 9.2 and higher Here is an example of a declaration of a varray and its instantiation: TYPE v_emp_type IS VARRAY (1000) OF emp%rowtype; emp_varray v_emp_type; You access both varrays and INDEX BY... SQL statements in data structures This leads to an abundance of plumbing and can make database interaction code cumbersome to write The SQL statements that you see appear to be nearly identical to the Oracle SQL that you’ve seen elsewhere in the table, but there are some important differences Not all of SQL can be used in PL/SQL Second, the SQL statements you use in PL/SQL—most significantly the SELECT . three chapters delve more deeply into the Oracle database technologies. The tech- nologies described are by no means an inclusive representation of the entire Oracle database; rather, they are the. appears. SELECT CONVERT(‘Ä Ê Í Õ Ø A B C D E ‘, ‘US7ASCII’, ‘WE8ISO8859P1’) AS convert_str FROM DUAL Oracle SQL 221 Table 8.108 lists the results. Table 8.108 Convert Results CONVERT_STR A E I ? ?. first expression otherwise. Nvl If an argument is null, replace it with the given value. (continues) Oracle SQL 223 Table 8.112 Miscelleneous Functions (Continued) NAME DESCRIPTION Nvl2 If the first