(vi) PL/SQL string

The PL/SQL string is actually an optional sequence of dimension-specification characters. A character can be a combination of numbers, letters, blanks, special characters, or all. PL/SQL provides three types of strings:
　　fixed-length string : In such a string, the programmer specifies the length while declaring the string. The string is the right padding space to reach the specified length.
variable length string : In such a string, the maximum length can be up to 32,767, specified for the string, and does not need to be populated.
　　character Large object (CLOB) : This is a variable-length string that can reach 128 megabytes.

The PL/SQL string can be a variable or literal value. String literals are enclosed inside the quotation marks. For example: ' This is a string literal. yiibai.com ' Or ' Hello World '
Text that includes single quotes in the string, requires two single quotes to be entered adjacent to each other, such as: ' This isn ' t what it looks like '

Declaration of a String variable
The Oracle database provides a number of string data types, such as: Char,nchar,varchar2,nvarchar2,clob and NCLOB. The data type preceded by an ' N ' is the "national character set" data type, which stores Unicode character data.
If you need to declare a variable-length string, you must provide the maximum length of the string. For example, the VARCHAR2 data type. The following example illustrates the declaration and use of some string variables:

DECLARE name VARCHAR2 ( -); Company VARCHAR2 ( -);   Introduction Clob; ChoiceChar(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 Smithinfotech Hello! I'm John Smith from Infotech.PL/sql procedure successfully completed

Two, PL/SQL string functions and operators
PL/SQL provides the join operator (| | ) is used to connect two strings. The following table provides the string functionality (functions) provided with PL/sql:

	functions and uses
1	ASCII (x); Returns the ASCII value of the character X
2	CHR (x); returns the ASCII value of the character X
3	CONCAT (x, y); Concatenate strings x and Y, and return additional strings
4	initcap (x); Each word is converted to uppercase in the first letter x, and the string is returned
5	INSTR (x, find_string [, start] [, occurrence]); Search find_string in X and return to where it appears
6	INSTRB (x); Returns the position of a string in 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 string of bytes for a single-byte character set
9	LOWER (x); converts an x to a lowercase letter and returns the string
10	lpad (x, Width [, pad_string]); X fills the left with a space, and the total length of the string reaches the wide character
11	LTRIM (x [, trim_string]); Left trim character from X
12	NANVL (x, value); If x matches the special value of Nan (not a number) it returns its value, otherwise it returns X
13	nls_initcap (x); The same initcap function, but it can be specified using a different sort method nlssort
14	nls_lower (x); Similarly, the difference is that it can be specified using a different sorting method nlssort lower function
15	nls_upper (x); The same, except that it can use different sorting methods to specify the Nlssort upper function
16	nlssort (x); The method of changing the sorted character. This parameter must be specified before any NLS function; otherwise, the default sort is used
17	NVL (x, value); Returns NULL if x is null; Otherwise, X is returned
18	NVL2 (x, value1, value2); If x is not NULL, return value1; If x is null, the value2 is returned
19	REPLACE (x, search_string, replace_string); Search x for search_string and replace with replace_string it
20	rpad (x, Width [, pad_string]); Fill x to the right
21st	RTRIM (x [, trim_string]); Trim from X Right
22	SOUNDEX (x); Returns a string containing the phonetic representation of X
23	SUBSTR (x, start [, length]); Returns a child of x starting at the position specified by start. Optional length is substring
24	SUBSTRB (x); Systems with single-byte characters in bytes instead of characters except for the same substr
25	TRIM ([Trim_char from) x); Trim x characters from left and right
26	UPPER (x); X is converted to uppercase and returns the string

(vi) PL/SQL string