Question

我有价值观 [abc,123,aed,ghi] 我想在mysql中单独拆分值。结果应该是这样的

column1 column2 column3 column4
  abc    123    aed      ghi

Answer 1

关系数据库和非原子数据设计很差。但你可以使用：

SELECT ID,
  MAX(CASE WHEN N = 1 THEN sub.val END) AS Column1,
  MAX(CASE WHEN N = 2 THEN sub.val END) AS Column2,
  MAX(CASE WHEN N = 3 THEN sub.val END) AS Column3,
  MAX(CASE WHEN N = 4 THEN sub.val END) AS Column4
FROM
(
  SELECT ID, SUBSTRING_INDEX(SUBSTRING_INDEX(t.HashTag, ',', n.n), ',', -1) AS val, N
  FROM (SELECT ID, Substring(my_csv_column, 2, LENGTH(my_csv_column) - 2) AS HashTag FROM my_non_normalized_table) AS t 
  CROSS JOIN 
  (
   SELECT a.N + b.N * 10 + 1 n
     FROM 
    (SELECT 0 AS N UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) a
   ,(SELECT 0 AS N UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) b
  ) n
   WHERE n.n <= 1 + (LENGTH(t.HashTag) - LENGTH(REPLACE(t.HashTag, ',', '')))
) sub
GROUP BY ID;

的 SqlFiddleDemo

输出：

╔═════╦══════════╦══════════╦══════════╦═════════╗ ║ ID ║ Column1 ║ Column2 ║ Column3 ║ Column4 ║ ╠═════╬══════════╬══════════╬══════════╬═════════╣ ║ 1 ║ abc ║ 123 ║ aed ║ ghi ║ ║ 2 ║ efg ║ cde ║ (null) ║ (null) ║ ╚═════╩══════════╩══════════╩══════════╩═════════╝

您应该阅读有关数据规范化和1NF。
的信息

Answer 2

不幸的是，MySQL没有分裂字符串功能。然而   您可以为此创建user defined function，例如一个   在下面的文章中描述：

  Federico Cargnelutti的
MySQL Split String Function


使用该功能，您可以按如下方式构建查询：

void test(int... values){}

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我有值（abc，123，aed，ghi），我想在我的sql中单独拆分值

2 个答案: