How to use the LPAD function in MySQL to left-pad a string to a specified length

How to use the LPAD function in MySQL to left-pad a string to a specified length

In the MySQL database, the LPAD function is a very useful function that can left-pad a string to a specified length. This function can be used for data processing and data conversion, and is especially suitable for scenarios where fixed-length strings need to be displayed. This article will detail how to use the LPAD function to achieve this functionality, with code examples.

The syntax of the LPAD function is as follows:
LPAD(str, len, pad_str)

str: ​​The string to be filled.
len: Specify the total length of the final string.
pad_str: String used for padding.

The following is a simple example, assuming we have a string "123" and want to left-pad it to a total length of 5 and the padding character is "0". The code example is as follows:
SELECT LPAD('123', 5, '0');

After executing the above code, the result will be "00123", that is, the left side of "123" will be filled with two "0", making its total length 5.

In addition to filling with fixed strings, the LPAD function also supports dynamic filling with other strings. The following is an example of code that shows how to use the LPAD function to left-pad a number to a specified number of digits:
SELECT LPAD(123, 6, '0');

After executing the above code, you will get The result is "000123", that is, three "0"s are padded to the left of the number 123, making its total length 6.

In addition, if the length of the string to be filled itself exceeds the length specified by len, the LPAD function will not truncate it. The following is an example showing the code for this situation:
SELECT LPAD('abcdefghij', 5, '0');

After executing the above code, the result will be "abcdefghij", that is The padding character "0" has no effect because the length of the string to be padded is already greater than the specified length.

In practical applications, the LPAD function is often used together with other functions to meet more complex requirements. For example, combined with the SUBSTR function, the result of the LPAD function can be intercepted to obtain the padding string at a specific position. Here is an example that shows how to use the LPAD function and the SUBSTR function to achieve this operation:
SELECT SUBSTR(LPAD('abc', 5, '0'), 3, 3);

After executing the above code, the result will be "00a", that is, the string "abc" will be left-padded to a length of 5, and then intercepted to obtain 3 characters starting from the 3rd character.

Summary:
The LPAD function is a very practical function in the MySQL database, which can left-fill a string to a specified length. Through the introduction of this article, we understand the syntax and common usage of the LPAD function, and provide code examples to help readers better understand and apply the LPAD function. It is hoped that readers can learn and use LPAD functions flexibly to improve the efficiency of data processing and conversion.

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