« Previous | 1 | 2 | 3 | Next »

Plsql - 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, like:

'this isn''t what it looks like'

Declaring String Variables

Oracle database provides numerous string datatypes , like, 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 SQL prompt, it produces the following result:

John Smith
Infotech Corporation
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. So following two declarations below 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:

S.N	Function & Purpose
1	ASCII(x); Returns the ASCII value of the character x.
2	CHR(x); Returns the character with the ASCII value of x.
3	CONCAT(x, y); Concatenates the strings x and y and return the appended string.
4	INITCAP(x); Converts the initial letter of each word in x to uppercase and returns that string.
5	INSTR(x, find_string [, start] [, occurrence]); Searches for find_string in x and returns the position at which it occurs.
6	INSTRB(x); Returns the location of a string within another string, but returns the value in bytes.
7	LENGTH(x); Returns the number of characters in x.
8	LENGTHB(x); Returns the length of a character string in bytes for single byte character set.
9	LOWER(x); Converts the letters in x to lowercase and returns that string.
10	LPAD(x, width [, pad_string]) ; Pads x with spaces to left, to bring the total length of the string up to width characters.
11	LTRIM(x [, trim_string]); Trims characters from the left of x.
12	NANVL(x, value); Returns value if x matches the NaN special value (not a number), otherwise x is returned.
13	NLS_INITCAP(x); Same as the INITCAP function except that it can use a different sort method as specified by NLSSORT.
14	NLS_LOWER(x) ; Same as the LOWER function except that it can use a different sort method as specified by NLSSORT.
15	NLS_UPPER(x); Same as the UPPER function except that it can use a different sort method as specified by NLSSORT.
16	NLSSORT(x); Changes the method of sorting the characters. Must be specified before any NLS function; otherwise, the default sort will be used.
17	NVL(x, value); Returns value if x is null; otherwise, x is returned.
18	NVL2(x, value1, value2); Returns value1 if x is not null; if x is null, value2 is returned.
19	REPLACE(x, search_string, replace_string); Searches x for search_string and replaces it with replace_string.
20	RPAD(x, width [, pad_string]); Pads x to the right.
21	RTRIM(x [, trim_string]); Trims x from the right.
22	SOUNDEX(x) ; Returns a string containing the phonetic representation of x.
23	SUBSTR(x, start [, length]); Returns a substring of x that begins at the position specified by start. An optional length for the substring may be supplied.
24	SUBSTRB(x); Same as SUBSTR except the parameters are expressed in bytes instead of characters for the single-byte character systems.
25	TRIM([trim_char FROM) x); Trims characters from the left and right of x.
26	UPPER(x); Converts the letters in x to uppercase and returns that string.

The following examples illustrate some of the above-mentioned functions and their use:

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 SQL prompt, it produces the following result:

HELLO WORLD
hello world
Hello World
h
d
Worl
d
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 SQL prompt, it produces the following result:

......Hello World
Hello World.....
Hello World
PL/SQL procedure successfully completed.

« Previous | 1 | 2 | 3 | Next »

The largest Interview Solution Library on the web

Plsql - Strings