mysql convert string

MySQL is a commonly used relational database management system. Sometimes we need to convert it into a string when processing data, because strings are a universal data type that facilitates data processing and storage. MySQL provides a variety of functions for converting data into strings, which this article will introduce.

1. Basic functions for converting MySQL to strings

1. CAST function

The CAST function can convert an expression into a string of a specified type , commonly used conversion types include char, varchar, text, etc. The syntax is as follows:

CAST(expression AS type)

where expression is the expression that needs to be converted, and type is the conversion type. For example:

SELECT CAST(12345 AS CHAR); --The output result is '12345'
SELECT CAST('123.45' AS DECIMAL(6,2)); --The output result is 123.45

2. CONVERT function

The CONVERT function can also convert an expression into a string of a specified type. It is similar to the CAST function. The syntax is as follows:

CONVERT( expression, type)

where expression is the expression that needs to be converted, and type is the conversion type. For example:

SELECT CONVERT(12345, CHAR); --The output result is '12345'
SELECT CONVERT('123.45', DECIMAL(6,2)); --The output result is 123.45

2. MySQL string function

1. CONCAT function

The CONCAT function can connect multiple strings. The syntax is as follows:

CONCAT(str1, str2, ...)

where str1, str2, ... are the strings that need to be connected, for example:

SELECT CONCAT('hello', 'world'); - -The output result is 'helloworld'
SELECT CONCAT('hello', ' ', 'world'); --The output result is 'hello world'

2. SUBSTRING function

SUBSTRING function can intercept a substring of specified length from a string. The syntax is as follows:

SUBSTRING(str, start, length)

where str is the character to be intercepted String, start is the starting position, length is the interception length, for example:

SELECT SUBSTRING('hello world', 1, 5); --The output result is 'hello'

3. REPLACE function

The REPLACE function can replace certain characters in a string with other characters. The syntax is as follows:

REPLACE(str, from_str, to_str)

Str is the string that needs to be replaced, from_str is the character that needs to be replaced, and to_str is the replaced character. For example:

SELECT REPLACE('hello world', 'world', 'jason'); --The output result is 'hello jason'

4. UPPER and LOWER functions

The UPPER and LOWER functions can convert all characters in a string to uppercase or lowercase letters respectively. The syntax is as follows:

UPPER(str)
LOWER(str)

Str is the string that needs to be converted, for example:

SELECT UPPER('hello world'); --The output result is 'HELLO WORLD'
SELECT LOWER('HELLO WORLD'); --The output result is 'hello world'

3. Convert MySQL date function to string

MySQL also provides some functions that can convert date types into strings. Commonly used ones are DATE_FORMAT function and CONVERT function. The specific usage is as follows:

1. DATE_FORMAT function

The DATE_FORMAT function can format the date and time into a specified string. The syntax is as follows:

DATE_FORMAT(date_time , format)

where date_time is the date and time that needs to be converted, format is the format that needs to be converted, for example:

SELECT DATE_FORMAT(NOW(), '%Y-%m-%d % H:%i:%s'); --The output result is '2022-01-01 00:00:00'

2. CONVERT function

CONVERT function also The date and time can be converted into a specified string. The syntax is as follows:

CONVERT(date_time, format)

where date_time is the date and time that needs to be converted, and format is the format that needs to be converted, for example:

SELECT CONVERT(NOW(), CHAR(20)); --The output result is '2022-01-01 00:00:00'

Summary

MySQL Provides a variety of functions for converting to strings to meet the needs of different scenarios. When using it, you need to choose the appropriate function according to the specific situation. At the same time, when converting strings, you also need to pay attention to issues such as data type and encoding to ensure the correctness and security of the data.

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