如何使用group_concat和conact，distinct引用单列的值

Question

我需要使用group_concat来构建一个用逗号分隔的值的列表，但是我需要在单引号内将这些值引起来。这该怎么做？我写的查询对我不起作用     实际上，我在这样的列中有值：

userid (column)

 1)   1,2
 2)   3,4

Query 1:

SELECT GROUP_CONCAT( DISTINCT CONCAT('\'', user_id, '\'') ) as listed_id

Query 2:
SELECT GROUP_CONCAT( DISTINCT CONCAT('''', user_id, '''') ) as listed_id

Expected out put:

   '1','2','3','4'

But I am getting values like this
   '1,2,3,4'

Answer 1

尝试一下，在我的情况下，它工作得很好：

void convert(char src[], char dest[]) {
    int i, isVowel, first_pos;
    int len = strlen(src);
    int count = 0;
    char first = 0;

    for (i = 0; i <= len; i++) {
        while (src[i] && !isspace(src[i])) {

            if (first == 0) {
                first = src[i];
                first_pos = i;
            }

            isVowel = first == 'a' || first == 'e' || first == 'i' || first == 'o' || first == 'u';

            if (isVowel == 1) {
                dest[count++] = src[i];
            }   
            else if (i != first_pos) {
                dest[count++] = src[i];
            }   

            i++;
        }   

        if (isVowel == 0) {
            dest[count++] = first;
        } 

        dest[count++] = ' ';
        first = 0;
      }
      dest[count++] = '\0';
}

这是输出：