Question

我似乎很反对这个问题，我的数据格式如下：

+----+----------------------+
| id | colors               |
+----+----------------------+
| 1  | Red,Green,Blue       |
| 2  | Orangered,Periwinkle |
+----+----------------------+

但我希望它的格式如下：

+----+------------+
| id | colors     |
+----+------------+
| 1  | Red        |
| 1  | Green      |
| 1  | Blue       |
| 2  | Orangered  |
| 2  | Periwinkle |
+----+------------+

这样做有好办法吗？什么是这种操作甚至叫做？

Answer 1

你可以使用这样的查询：

SELECT
  id,
  SUBSTRING_INDEX(SUBSTRING_INDEX(colors, ',', n.digit+1), ',', -1) color
FROM
  colors
  INNER JOIN
  (SELECT 0 digit UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3) n
  ON LENGTH(REPLACE(colors, ',' , '')) <= LENGTH(colors)-n.digit
ORDER BY
  id,
  n.digit

请参阅小提琴here。请注意，此查询每行最多支持4种颜色，您应该更新子查询以返回4个以上的数字（或者您应该使用包含10或100个数字的表格）。

Answer 2

我认为这是你需要的（存储过程）：Mysql split column string into rows

DELIMITER $$

DROP PROCEDURE IF EXISTS explode_table $$
CREATE PROCEDURE explode_table(bound VARCHAR(255))

BEGIN

DECLARE id INT DEFAULT 0;
DECLARE value TEXT;
DECLARE occurance INT DEFAULT 0;
DECLARE i INT DEFAULT 0;
DECLARE splitted_value INT;
DECLARE done INT DEFAULT 0;
DECLARE cur1 CURSOR FOR SELECT table1.id, table1.value
                                     FROM table1
                                     WHERE table1.value != '';
DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = 1;

DROP TEMPORARY TABLE IF EXISTS table2;
CREATE TEMPORARY TABLE table2(
`id` INT NOT NULL,
`value` VARCHAR(255) NOT NULL
) ENGINE=Memory;

OPEN cur1;
  read_loop: LOOP
    FETCH cur1 INTO id, value;
    IF done THEN
      LEAVE read_loop;
    END IF;

    SET occurance = (SELECT LENGTH(value)
                             - LENGTH(REPLACE(value, bound, ''))
                             +1);
    SET i=1;
    WHILE i <= occurance DO
      SET splitted_value =
      (SELECT REPLACE(SUBSTRING(SUBSTRING_INDEX(value, bound, i),
      LENGTH(SUBSTRING_INDEX(value, bound, i - 1)) + 1), ',', ''));

      INSERT INTO table2 VALUES (id, splitted_value);
      SET i = i + 1;

    END WHILE;
  END LOOP;

  SELECT * FROM table2;
 CLOSE cur1;
 END; $$

Answer 3

不需要存储过程。一个 CTE 就足够了：

CREATE TABLE colors(id INT,colors TEXT);
INSERT INTO colors VALUES (1, 'Red,Green,Blue'), (2, 'Orangered,Periwinkle');

WITH RECURSIVE
  unwound AS (
    SELECT *
      FROM colors
    UNION ALL
    SELECT id, regexp_replace(colors, '^[^,]*,', '') colors
      FROM unwound
      WHERE colors LIKE '%,%'
  )
  SELECT id, regexp_replace(colors, ',.*', '') colors
    FROM unwound
    ORDER BY id
;

+------+------------+
| id   | colors     |
+------+------------+
|    1 | Red        |
|    1 | Green      |
|    1 | Blue       |
|    2 | Orangered  |
|    2 | Periwinkle |
+------+------------+

Answer 4

这节省了我很多时间！更进一步：在一个典型的实现中，很可能会有一个表格，它根据身份密钥color_list枚举颜色。可以在不必修改查询的情况下向实现添加新颜色，并且可以通过将查询更改为此来完全避免可能无限的union -clause：

SELECT id,
  SUBSTRING_INDEX(SUBSTRING_INDEX(colors, ',', n.digit+1), ',', -1) color
FROM
  colors
  INNER JOIN
  (select id as digit from color_list) n
  ON LENGTH(REPLACE(colors, ',' , '')) <= LENGTH(colors)-n.digit
ORDER BY id, n.digit;

然而，表color_list中的Ids保持顺序非常重要。

Answer 5

请注意，这可以在不创建临时表的情况下完成

select id, substring_index(substring_index(genre, ',', n), ',', -1) as genre
from my_table
join 
(SELECT @row := @row + 1 as n FROM 
(select 0 union all select 1 union all select 3 union all select 4 union all select 5 union all select 6 union all select 6 union all select 7 union all select 8 union all select 9) t,
(SELECT @row:=0) r) as numbers
  on char_length(genre) 
    - char_length(replace(genre, ',', ''))  >= n - 1

Answer 6

如果定界符是数据的一部分但用双引号括起来，那么我们如何分割它。

示例第一，第二，第三

它应该作为第一秒第三

MySQL中GROUP_CONCAT的反义词是什么？

6 个答案: