MySQL String function usage tips

1. Intercept string from left
Left (str, length)
Description: Left (truncated field, intercept length)
Example: Select Left (content,200) as abstract from my_content_t

2, starting from the right to intercept the string
Right (str, length)
Description: Right (truncated field, intercept length)
Example: Select Right (content,200) as abstract from my_content_t

3. Intercepting strings
SUBSTRING (str, POS)
SUBSTRING (str, pos, length)
Description: Substring (intercepted field, starting from the first intercept)
SUBSTRING (intercepted field, starting from the first intercept, intercept length)
Example: Select substring (content,5) as abstract from my_content_t
Select substring (content,5,200) as abstract from my_content_t
(Note: If the number of digits is negative, 5 is the number of digits from the back to the end of the string or the length of the Intercept)

4. Intercept strings by keyword
Substring_index (Str,delim,count)
Description: Substring_index (the number of occurrences of the intercepted field, keywords, keywords)
Example: Select Substring_index ("Blog.jb51.net", ". ", 2) as abstract from my_content_t
Results: blog.jb51
(Note: If the number of occurrences of a keyword is negative, 2 is the inverse from the back to the end of the string)

5, INSTR (STR,SUBSTR); LOCATE (STR,SUBSTR); POSITION (str in substr)

Returns the position of the first occurrence of a substring substr in the string str. This is the same as the locate () with 2 parameters, except that the parameters are reversed.

6, REVERSE (str)

Reverse str;

7. TRUNCATE (x,d);

Returns the number x that is removed to the D-digit after the decimal point. If the value of D is 0, the result does not have a decimal point or a fractional part. D can be set to a negative number to intercept (zero) the value of all lows after the beginning of the D bit of the decimal point.
Today there is a need to query the percentage of a 2 field in a standard table ....

Example:

Select TRUNCATE (progress/video_duration,2) as percent from  mime_study_logs;

The Video_duration field even if (the denominator here is 0 or null), the return is also null, without using PHP to verify the legality of the Division

This calculates the division of two numbers, and 2 indicates the number of digits following the decimal point, for example: 1/3 =0.33

MySQL String function usage tips