SQL substring_index() usage - MySQL string interception

Table of Contents

1. The syntax of the substring_index function and its usage

(1) Syntax: substring_index(string,sep,num)

(2) is used to intercept the target string.

2.Instance

(1) From aField intercepts the target string.

(2) Used in conjunction with the cast function to intercept a string and convert it to the target format.

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1.The syntax of the substring_index function and its usage

(1) Syntax: substring_index(string,sep,num)

That is, substring_index (string, separator, serial number)

Parameter description

string: The string used to intercept the target string.Can be fields, expressions, etc.

sep: Separator, a character that exists and is used to separate strings, such as ",", ".", etc.

num: serial number, which is a non-zero integer.If it is an integer, it counts from left to right, and if it is a negative number, it counts from right to left.For example, "www.mysql.com" intercepts the character 'www', the separator is ".", and the sequence number from left to right is 1, that is, substring_index("www.mysql.com",'.',1);To start getting "com", the serial number is -1, that is, substring_index("www.mysql.com",'.',-1)

(2) is used to intercept the target string.

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2.Instance

(1) Intercept the target string from a field.

Example: There is a student information table student, and the detailed address address stores the address information separated by commas such as province, city, county, such as "XX province, XX city, XX district, ..., XXX number".For some reason, there is no information about the province where the student is located. At the same time, the student's name, gender, and age are obtained.

select name,sex,age,substring_index(address,',',1) as provincefrom student

(2) Combine with the cast function to intercept a string and convert it to the target format.

Example: There is an existing order information data. Since the format of the date information stored after the date of 2022-03-04 is wrong, some prefixes are added before the date and separated by spaces, such as "13d 2022-02-01".Obtain the specific date information after 2022-03-04 in the table, and obtain the list offer_id and product name at the same time.

select cast(substring_index(ctime,' ',1) as date) as dt,offer_id,nameFROM dataWHERE substring_index(ctime,' ',1)>= '2022-03-04'

For the usage of cast function in SQL, please refer toSQL's CAST() - Converting Data Types_'s Blog-CSDN Blog

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