Top 30 SQL String Functions with Usage and Syntax

Detailed explanation of SQL string function: Swiss Army Knife for Database Text Processing

Think of SQL string functions as Swiss Army knives for database text processing. They are powerful tools for segmenting, organizing, cleaning or converting text data. Whether you're a developer trying to sort out cluttered user input or an analyst preparing to report data, these functions can help you. But what exactly is SQL string function? Need to concatenate two paragraphs of text together? There are corresponding functions. Want to extract only part of a long string? No problem, it can be done. Isn't it very attractive?

Can you also convert everything to capitalization, or look for specific words in a sentence? SQL string functions can handle all of this and more. They are unknown heroes in data collation, and they make our lives easier when processing text in databases. In this article, we will discuss SQL string functions in detail.

Overview

• Explore SQL string functions for text operations and data conversion in databases.
• Learn basic SQL string functions extracted from concatenation to substrings.
• Learn about the performance of optimizing SQL string operations and best practices for handling data types.
• Discover 30 powerful SQL string functions, including syntax and actual examples.
• Master SQL string functions to efficiently clean, analyze and database reporting.

Table of contents

• The importance of string functions
• Best practices for using string functions
• String functions in SQL
• Frequently Asked Questions

The importance of string functions

The importance of string functions in SQL cannot be overemphasized. They play a vital role in:

• Data Cleanup: Delete unwanted characters, standardize formats, and correct inconsistencies in text data.
• Data conversion: Convert data from one format to another, such as changing date formats or extracting specific string parts.
• Text Analysis: Perform operations such as calculating the number of occurrences of substrings or finding specific patterns in text.
• Report: Format text data for better reading and rendering in reports.
• Search function: Implement application search function by matching patterns or keywords in text fields.

Best practices for using string functions

• Performance: Some string functions can be computationally expensive, especially on large datasets. Use them with caution and consider indexing strategies when appropriate.
• Data Type: Make sure to use the correct data type for string columns (e.g. VARCHAR vs. NVARCHAR for Unicode support).
• Null value processing: Note how each function handles NULL values ​​and use COALESCE or ISNULL if necessary.
• Sorting rules: Understand the impact of database and column sorting rules on string operations, especially in multi-language environments.
• Test: Thoroughly test your string operations, especially when it comes to edge cases and special characters.

Let's explore a comprehensive list of string functions, including their usage, syntax, and examples.

String functions in SQL

Here are 30 SQL string functions:

(Some functions are listed below. Due to space limitations, all 30 functions and their examples cannot be listed.)

1. ASCII (US Standard Code for Information Exchange)

Usage: Returns the ASCII value of a specific character. Syntax: ASCII(character)

 SELECT ASCII('A') AS ascii_value;

<code>结果：65</code>

2. CHAR (character)

Usage: Return characters according to ASCII code. Syntax: CHAR(ascii_code)

 SELECT CHAR(65) AS character;

<code>结果：'A'</code>

3. CHARINDEX function

Usage: Returns the position of the substring. Syntax: CHARINDEX(substring, string [, start_position])

 SELECT CHARINDEX('World', 'Hello World') AS position;

<code>结果：7</code>

(The remaining function examples are omitted, but the function name and brief function description are retained)

4. CONCAT function: Concatenate two or more strings.
5. Use operators to join: Use operators to join two or more strings.
6. CONCAT_WS function: Use a delimiter to concatenate two or more strings.
7. DATALENGTH function: Returns the number of bytes representing the expression.
8. DIFFERENCE function: Compare two SOUNDEX values ​​and return an integer value.
9. FORMAT function: Format the value using the specified format.
10. LEFT function: Extract a certain number of characters from a string (starting from the left).
11. LEN function: Returns the length of the string.
12. LOWER function: Converts a string to lowercase.
13. LTRIM function: Removes the space at the beginning of the string.
14. NCHAR function: Returns Unicode characters based on numeric code.
15. PATINDEX function: Returns the position of the pattern in the string.
16. QUOTENAME function: Returns a Unicode string with delimiter added to make it a valid SQL Server delimited identifier.
17. REPLACE function: Replace all occurrences of substrings in the string with a new substring.
18. REPLICATE function: repeat the string multiple times.
19. REVERSE function: Inverts the string and returns the result.
20. RIGHT function: Extract a certain number of characters from a string (starting from the right).
21. RTRIM function: Removes the space at the end of the string.
22. SOUNDEX function: Returns a four-character code to evaluate the similarity of two strings.
23. SPACE function: Returns a string of the specified number of space characters.
24. STR function: Returns a number as a string.
25. STUFF function: Delete part of the string, and then insert another part into the string, starting at the specified location.
26. SUBSTRING function: Extract some characters from a string.
27. TRANSLATE function: Convert the character specified in the first parameter to the character in the second parameter to the character in the third parameter to the result.
28. TRIM function: Removes spaces (or other specified characters) at the beginning and end of a string.
29. UNICODE function: Returns the Unicode value of the first character of the input expression.
30. UPPER function: Converts a string to uppercase.

in conclusion

The functions mentioned in this article can handle many tasks related to string operations. Note that the actual syntax and availability of functions in different database management systems such as MySQL or Postgres may vary slightly, and it is best to consult your DBMS documentation for details on these functions.

Frequently Asked Questions

Q1. What is a string function in SQL?

A1. String functions in SQL are predefined functions that help manipulate, change, or retrieve text data (strings) stored in a database. These operations can include string concatenation and substring extraction, changing case, and finding patterns in string values.

Q2. How to use string functions in SQL?

A2. To use a string function in SQL, it is usually included in a SELECT statement or a WHERE clause. The general syntax is as follows: SELECT string_function(column_name) FROM table_name; For example: SELECT UPPER(first_name) FROM employees;

Q3. How to get the first 10 characters of a string in SQL?

A3. You can use the LEFT function or SUBSTRING function to extract the first 10 characters from a string: Use LEFT: SELECT LEFT(column_name, 10) FROM table_name; Use SUBSTRING: SELECT SUBSTRING(column_name, 1, 10) FROM table_name;

Q4. What are some common string functions?

A4. Some commonly used string functions in SQL include:

1. CONCAT: Combining two or more strings
2. UPPER/LOWER: Convert text to uppercase or lowercase
3. LENGTH/LEN: Return the length of the string
4. SUBSTRING: Extract part of a string
5. TRIM: Remove the beginning and end spaces
6. REPLACE: The occurrence of replacement substring
7. LEFT/RIGHT: Extract characters from the left or right side of the string

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