MySQL - 如何从所有记录中获取特定值的计数

Question

I have course table and I am storing completion status of users with 'A'. Now I want to get how many A is available from CompletionStatus field for all records.

I want this result: A = 5.

Course Table:

CourseRecordIdx     User    CompletionStatus 
---------------     ----    --------------------
1                   152     A___A_______________
2                   147     AA_______A__________

I have tried with char_length but getting count with underscore and I want to get only total of A :

SELECT char_length(CompletionStatus) FROM `course` where CourseRecordIdx = 36

Any idea how to get result with select query?

Thanks.

Answer 1

You can use LENGTH and REPLACE for that purpose :

SELECT LENGTH(CompletionStatus) - LENGTH(REPLACE(CompletionStatus, 'A', '')) as count_Char
 FROM `course`

This basically counts how many characters are in that string, and then checks the difference between that number, and the number of characters with out the specific character.

Answer 2

您可以尝试这种最简单的方法：

 SELECT length(REPLACE("field_name","_","")) FROM `tbl_name`;

Answer 3

I suppose the following will work, first replace all _ with '' . After that use char_length() function.

SELECT CHAR_LENGTH(REPLACE(CompletionStatus,'_','') as totalA FROM course where CourseRecordIdx = 36;

Answer 4

You can write this query for this:

SELECT CourseRecordIdx,User,CompletionStatus,
ROUND (   
    (
    LENGTH(CompletionStatus)- LENGTH( REPLACE ( CompletionStatus, "A", "")) 
    ) / LENGTH("A")) AS count    
from `course` where CourseRecordIdx = 36