PL/SQL - Strings

The string in PL/SQL is actually a sequence of characters with an optional size specification. The characters could be numeric, letters, blank, special characters or a combination of all. PL/SQL offers three kinds of strings −

• Fixed-length strings − In such strings, programmers specify the length while declaring the string. The string is right-padded with spaces to the length so specified.

• Variable-length strings − In such strings, a maximum length up to 32,767, for the string is specified and no padding takes place.

• Character large objects (CLOBs) − These are variable-length strings that can be up to 128 terabytes.

PL/SQL strings could be either variables or literals. A string literal is enclosed within quotation marks. For example,

'This is a string literal.' Or 'hello world'

To include a single quote inside a string literal, you need to type two single quotes next to one another. For example,

'this isn''t what it looks like'

Declaring String Variables

Oracle database provides numerous string datatypes, such as CHAR, NCHAR, VARCHAR2, NVARCHAR2, CLOB, and NCLOB. The datatypes prefixed with an 'N' are 'national character set' datatypes, that store Unicode character data.

If you need to declare a variable-length string, you must provide the maximum length of that string. For example, the VARCHAR2 data type. The following example illustrates declaring and using some string variables −

DECLARE 
   name varchar2(20); 
   company varchar2(30); 
   introduction clob; 
   choice char(1); 
BEGIN 
   name := 'John Smith'; 
   company := 'Infotech'; 
   introduction := ' Hello! I''m John Smith from Infotech.'; 
   choice := 'y'; 
   IF choice = 'y' THEN 
      dbms_output.put_line(name); 
      dbms_output.put_line(company); 
      dbms_output.put_line(introduction); 
   END IF; 
END; 
/

When the above code is executed at the SQL prompt, it produces the following result −

John Smith 
Infotech
Hello! I'm John Smith from Infotech.  

PL/SQL procedure successfully completed

To declare a fixed-length string, use the CHAR datatype. Here you do not have to specify a maximum length for a fixed-length variable. If you leave off the length constraint, Oracle Database automatically uses a maximum length required. The following two declarations are identical −

red_flag CHAR(1) := 'Y'; 
 red_flag CHAR   := 'Y';

PL/SQL String Functions and Operators

PL/SQL offers the concatenation operator (||) for joining two strings. The following table provides the string functions provided by PL/SQL −

Let us now work out on a few examples to understand the concept −

Example 1

DECLARE 
   greetings varchar2(11) := 'hello world'; 
BEGIN 
   dbms_output.put_line(UPPER(greetings)); 
    
   dbms_output.put_line(LOWER(greetings)); 
    
   dbms_output.put_line(INITCAP(greetings)); 
    
   /* retrieve the first character in the string */ 
   dbms_output.put_line ( SUBSTR (greetings, 1, 1)); 
    
   /* retrieve the last character in the string */ 
   dbms_output.put_line ( SUBSTR (greetings, -1, 1)); 
    
   /* retrieve five characters,  
      starting from the seventh position. */ 
   dbms_output.put_line ( SUBSTR (greetings, 7, 5)); 
    
   /* retrieve the remainder of the string, 
      starting from the second position. */ 
   dbms_output.put_line ( SUBSTR (greetings, 2)); 
     
   /* find the location of the first "e" */ 
   dbms_output.put_line ( INSTR (greetings, 'e')); 
END; 
/ 

When the above code is executed at the SQL prompt, it produces the following result −

HELLO WORLD 
hello world 
Hello World 
h 
d 
World 
ello World 
2  

PL/SQL procedure successfully completed.

Example 2

DECLARE 
   greetings varchar2(30) := '......Hello World.....'; 
BEGIN 
   dbms_output.put_line(RTRIM(greetings,'.')); 
   dbms_output.put_line(LTRIM(greetings, '.')); 
   dbms_output.put_line(TRIM( '.' from greetings)); 
END; 
/

When the above code is executed at the SQL prompt, it produces the following result −

......Hello World  
Hello World..... 
Hello World  

PL/SQL procedure successfully completed.