GROUP_CONCAT mysql 语句错误

Question

我已经尝试了 mysql ststement 用于动态行到列，然后在此处使用查询语句：

SET @sql = NULL;
SELECT 
GROUP_CONCAT(DISTINCT
  CONCAT(
    'MAX(CASE WHEN col = ''', 
    col,
    ''' THEN val END) as `',
    col, '`'
  )
)INTO @sql
FROM
(
   SELECT A.id_a, D.id_c id_c,
          C.students students,
          CONCAT(B.`code`, '_', A.id_a) col,
          CONCAT(D.value_m, ',', D.value_n) val
  FROM table_a A
      INNER JOIN table_d D ON A.id_a =D.id_a
      INNER JOIN table_b B ON D.id_b=B.id_b 
      INNER JOIN table_c C ON D.id_c=C.id_c
)dd;

SET @sql = CONCAT('SELECT id_c, students,', @sql, '
        FROM(
            SELECT A.id_a, D.id_c id_c,
                C.students students,
                CONCAT(B.`code`, '_', A.id_a) col,
                CONCAT(D.value_m, ',', D.value_n) val
            FROM table_a A
                INNER JOIN table_d D ON A.id_a =D.id_a
                INNER JOIN table_b B ON D.id_b=B.id_b 
                INNER JOIN table_c C ON D.id_c=C.id_c
        )dd 
        GROUP BY id_c'
    );

PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

结果消息：

Query OK, 0 rows affected
Query OK, 1 row affected
1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '', A.id_a) col,
            CONCAT(D.value_m, ',', D.value_n) val
        FROM table_a A    ' at line 1
1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'MAX(CASE WHEN col = 'MAT_1' THEN val END) as `MAT_1`,MAX(CASE WHEN col = 'BIO_1'' at line 1
1243 - Unknown prepared statement handler (stmt) given to EXECUTE
1243 - Unknown prepared statement handler (stmt) given to DEALLOCATE PREPARE

我不熟悉这样的 sql 语句，那个 SQL QUERY 有什么问题

谢谢...

Answer 1

如果您查看代码（并放大）：

SET @sql = CONCAT('SELECT id_c, students,', @sql, '
        [..]
                CONCAT(B.`code`, '_', A.id_a) col,
                CONCAT(D.value_m, ',', D.value_n) val
        [..]
        GROUP BY id_c'
    );

您会看到_和,是黑色的，而作为字符串的一部分，它们应该是红色的。 这意味着您的字符串在那里“断裂”。 所以你需要用''转义单引号：

SET @sql = CONCAT('SELECT id_c, students,', @sql, '
        [..]
                CONCAT(B.`code`, ''_'', A.id_a) col,
                CONCAT(D.value_m, '','', D.value_n) val
        [..]
        GROUP BY id_c'
    );

或者对包含单引号的字符串使用双引号：

SET @sql = CONCAT('SELECT id_c, students,', @sql, "
        [..]
                CONCAT(B.`code`, '_', A.id_a) col,
                CONCAT(D.value_m, ',', D.value_n) val
        [..]
        GROUP BY id_c"
    );

现在完整的字符串是红色的，因为它应该是:-)

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