SQL String Functions: Overview

A function that accepts a string value as an input irrespective of the data type of the returned value is known as a string function. There is a wide range of built-in SQL string functions in the SQL Server for developers to use. This article will present a list of the most commonly used SQL string functions that make programming in SQL easier. 

Commonly Used SQL String Functions

ASCII

The first SQL string function we’ll look at is ASCII(). This scalar function works by accepting a given string as input and returning the corresponding ASCII code for the first character in that string. Using this SQL string function, we can find out the numeric value of the string’s leftmost character. In case the string is empty, it will return 0. If the string is null, the function will return NULL as output. 

Under the ASCII function, characters having numeric values ranging from 0 to 255 can be identified.

CHARLENGTH()

Using this function, the length of the string, which is calculated in characters, can be found. A multibyte character is treated as if it were a single character. This implies that the function LENGTH() presents as output 20 for a string with ten two-byte characters, whereas CHAR LENGTH() returns 10.

CONCAT

CONCAT() is another scalar SQL string function that accepts multiple strings as input and returns as output a single string after concatenating them all.

There might be one or many arguments. There are a maximum of 254 inputs that are allowed for this function. The result of CONCAT SQL will be a non-binary string if all input parameters are non-binary strings. However, the result is a binary string if any of the parameters are binary strings. If you don’t wish for a numeric input parameter to return its binary text counterpart.

CONCAT_WS()

CONCAT WS() is a special form of CONCAT that stands for Concatenate With Separator (). It’s identical to the CONCAT() function, except it lets you define a separator between the concatenated text. It may be used to create values separated by commas. The first argument serves as a divider between the other arguments. 

Between the strings to be concatenated, a separator is added. Like the rest of the inputs, the separator can be a string. The answer is NULL if the separator is NULL.

TRIM

The TRIM() function removes all prefixes and suffixes from the string. BOTH  is assumed if none of the specifiers BOTH, LEADING or TRAILING is specified. Spaces are eliminated if they are not mentioned otherwise. Here’s an example to illustrate the TRIM function:

SQL> SELECT TRIM(‘  bar   ‘);

+———————————————————+

| TRIM(‘  dog   ‘)                                        |

+———————————————————+

|  dog                                                       |

+———————————————————+

1 row in set (0.00 sec)

SQL> SELECT TRIM(LEADING ‘r’ FROM ‘rrrrrdogrrrrr’);

+———————————————————+

| TRIM(LEADING ‘r’ FROM rrrrr’dogrrrrr’)                      |

+———————————————————+

| dogrrrrr                                                  |

+———————————————————+

1 row in set (0.00 sec)

SQL> SELECT TRIM(BOTH ‘rx’ FROM ‘rrrrrdogrrrrr’’);

+———————————————————+

| TRIM(BOTH ‘r’ FROM ‘rrrrrdogrrrrr’)                         |

+———————————————————+

| dog                                                       |

+———————————————————+

1 row in set (0.00 sec)

SQL> SELECT TRIM(TRAILING ‘xyz’ FROM ‘dogrrrrxyz’);

+———————————————————+

| TRIM(TRAILING ‘xyz’ FROM ‘dogrrrrrrxyz’)                     |

+———————————————————+

| dogrrrrr                                                    |

+———————————————————+

1 row in set (0.00 sec)

SOUNDEX()

SOUNDEX() is a one-dimensional scalar function. SOUNDEX() is mostly used to match strings and link rows together. Soundex strings should be identical for two strings that sound almost identical. It takes a string as input and generates a four-character string based on how that string is pronounced. 

However, The SOUNDEX() function returns a string of a somewhat long and random length. To get a typical Soundex string, use SUBSTRING() on the result. The first character of the code is transformed to upper case from the first character of the input string. 

The code’s remaining characters are integers that represent the expression’s letters. A, O, U, E, I, Y, H, W) are the only letters that are not disregarded (unless they are the initial letter). Additional zeros are appended to the returned result if the string length is less than 4. Outside of the A-Z range, all international alphabetic letters are considered as vowels.

LOWER/UPPER

A typical SQL string function for changing the character case of an input string is the LOWER() and UPPER() functions. The functions LOWER() and UPPER() are used to modify the letter case to lowercase and uppercase, respectively.

LEFT/RIGHT

One of the most often used SQL string functions is the LEFT() and RIGHT() functions. They’re used to extract a certain amount of characters from a string’s left or right side.

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SUBSTRING_INDEX()

SQL Substring function returns the substring from the string before counting delimiter occurrences. While counting from the left, everything to the left of the last delimiter is returned if the count is positive. While counting from the right, everything to the right of the last delimiter is returned if the count is negative. When looking for delim, SUBSTRING INDEX() uses a case-sensitive match.

SQL> SELECT SUBSTRING(‘genetically’,5);

+———————————————————+

| SSUBSTRING(‘Genetically’,5)                           |

+———————————————————+

| tically                                               |

+———————————————————+

1 row in set (0.00 sec)

SQL> SELECT SUBSTRING(‘Welighed on’ barbarb 4);

+———————————————————+

| SUBSTRING(‘genetically’ FROM 4)                           |

+———————————————————+

| etically                                                  |

+———————————————————+

1 row in set (0.00 sec)

SQL> SELECT SUBSTRING(‘genetically’,5,6);

+———————————————————+

| SUBSTRING(‘genetically’,5,6)                          |

+———————————————————+

| ticall                                                |

+———————————————————+

1 row in set (0.00 sec)

SUBSTRING_INDEX(str,delim,count)

It returns the substring from “str” before count occurrences of delim. If the count is positive, everything to the left of the final delimiter (counting from the left) is returned. If the count is negative, everything to the right of the final delimiter (counting from the right) is returned. SUBSTRING_INDEX() performs a case-sensitive match when searching for delim.

SQL> SELECT SUBSTRING_INDEX(‘www.mysql.com’, ‘.’, 2);

+———————————————————+

| SUBSTRING_INDEX(‘www.mysql.com’, ‘.’, 2)                |

+———————————————————+

| www.mysql                                               |

+———————————————————+

1 row in set (0.00 sec)

The following table provides an overview of the string functions. 

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Conclusion

Through this article, we’ve sought to throw light on the various SQL string functions that developers can use when programming in SQL. Given that there is a growing need for Database Management Systems across industries, it is a great time for budding SQL developers to learn SQL to secure a lucrative career in the field.

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