The use of instr, rtrim, XMLPARSE, XMLAGG, GETCLOBVAL functions in Oracle

1：INSTR()函数

INSTRis a string function used to find the position of a substring in a source string .

Its syntax is as follows:

INSTR(source_string, search_string)

• source_stringis the source string, the string within which to search.
• search_stringis the substring to be found.

INSTRThe function returns the position of the first occurrence of the substring. If the substring is found, the return value is its index in the source string; if not found, 0 is returned.

Example:

 instr(XSXX.XM,#{studentName,jdbcType=VARCHAR})> 0

In the given code, INSTR(XSXX.XM, #{studentName, jdbcType=VARCHAR}) > 0it means XSXX.XMto find the substring in this string #{studentName, jdbcType=VARCHAR}and determine whether the position of the substring in the source string is greater than 0.

This expression is usually used in SQL query statements in databases to check whether a field contains a specific substring. In this case, INSTRthe position value returned by the function is greater than 0, indicating that the specified substring is contained in the field.

2：rtrim()function

rtrim()function is a string processing function that removes a specified character (or set of characters) from the end of a string.

Specifically, rtrim()the function does the following:

1. Receives a string as input parameter.
2. Starting from the end of the string, each character is checked to see if it belongs to the specified character set.
3. Once a character that does not belong to the specified character set is encountered, processing stops and the processed string is returned.
4. If the characters at the end of the string belong to the specified character set, an empty string will be returned.

You can use rtrim()the function to remove invisible characters such as spaces, tabs, newlines, etc. at the end of a string. You can also specify a custom character set to remove other specified characters.

Here is an example of using rtrim()the function to remove spaces from the end of a string:

SELECT RTRIM('Hello World     ');

The output is:

'Hello World'

In this example, rtrim()the function removes 'Hello World 'extra spaces from the end of the string and returns the string 'Hello World'.

To summarize, rtrim()the function of the function is to remove the specified characters (or character set) at the end of the string and return the processed string.

3：XMLPARSE()函数

XMLPARSE()Functions are used to parse XML data into values ​​of type XML. It can parse string, text, or binary data containing XML content into an XML type that can be processed and queried in a database.

Suppose we have an XML string representing a simple student information:

<Student>
   <Name>John Doe</Name>
   <Age>25</Age>
   <Major>Computer Science</Major>
</Student>

We can use XMLPARSE()the function to parse this string into an XML type value as follows:

SELECT XMLPARSE(CONTENT '<Student>
                          <Name>John Doe</Name>
                          <Age>25</Age>
                          <Major>Computer Science</Major>
                       </Student>') AS StudentXML;

The above query will return a result set of type XML containing the parsed XML data.

4：XMLAGG()函数

Suppose there is a table studentscontaining nameand gradecolumns, we can use XMLAGGthe function to splice each student's name into an XML document

SELECT XMLAGG(XMLELEMENT(E, name)) AS student_names
FROM students;

The output may look similar to:

<student_names>
  <E>John</E>
  <E>Alice</E>
  <E>Bob</E>
</student_names>

5：GETCLOBVAL()函数

Suppose there is an XML document parsed_xmlstored as CLOB type, we can use GETCLOBVALthe function to convert it to a CLOB value.

SELECT GETCLOBVAL(parsed_xml) AS clob_data
FROM my_table;