Join/Union 不同的列没有重复（Distinct）到一个新的 table

Question

尝试了几个小时，但未能找到可行的解决方案。我正在使用 MariaDB。我有一个包含数百万行 (MySourceTable) 的 table，我想从其中获取特定列的唯一单元格值，并将它们复制到新的 table.

COL_A  COL_B  COL_C  COL_D  COL_E

  1      11     a      ab     a1  
  2      12     a      cd     a2  
  3      13     a      ab     a3  
  1      14     b      ab     a2  
  2      12     c      ef     a5  
  4      15     d      gh     a1

新的内容应该是这样的：

COL_A   COL_B  COL_C  COL_D  COL_E

  1      11     a      ab     a1  
  2      12     b      cd     a2  
  3      13     c      ef     a3  
  4      14     d      gh     a5  
         15

是的 - 列在加入后不再有任何关系。需要新目标 table 中此特定列的唯一行，以便以后在 DataTables SearchPanes filter.

中使用它们

编辑：This 是数据table 搜索窗格期望过滤器值的方式。如果我不将列值区分为一个新的唯一 table，searchPanes 必须在每个页面上刷新到几千行，以获取值。

到目前为止我尝试了什么：

DROP TABLE IF EXISTS col_names;
CREATE Table col_names 
(
    /*ID MEDIUMINT NOT NULL AUTO_INCREMENT, */
    ID MEDIUMINT NOT NULL Auto_Increment, 
    COL_A TINYTEXT, 
    COL_B TINYTEXT, 
    COL_C TINYTEXT, 
    COL_D TINYTEXT, 
    COL_E TINYTEXT
    PRIMARY KEY (ID)
);

INSERT INTO col_names (COL_A)
    Select Distinct Source_A AS COL_A FROM MySourceTable;
INSERT INTO col_names (COL_B)
    Select Distinct Source_B AS COL_B FROM MySourceTable;
INSERT INTO col_names (COL_C)
    Select Distinct Source_C AS COL_C FROM MySourceTable;
INSERT INTO col_names (COL_D)
    Select Distinct Source_D AS COL_D FROM MySourceTable;
INSERT INTO col_names (COL_E)
    Select Distinct Source_E AS COL_E FROM MySourceTable;

SELECT * FROM col_names
    ORDER BY COL_A, COL_B Desc;

结果不是我所期待的。我认为，我必须使用 Cross Apply、Join、Union 等。尝试过不同的东西，但失败了很多次。

Answer 1

将您的要求更改为标准化输出；两列 - column_name 和 column_value。然后，您预期结果中的每个单元格都会成为规范化结构中的一行。这更符合 sql，更灵活，如果一列的值比其他列多得多，则不会出现奇怪的行为，等等

SELECT
  DISTINCT
  lookup.*
FROM
  MySourceTable
CROSS APPLY
(
  SELECT 'COL_A', MySourceTable.Source_A
  UNION ALL
  SELECT 'COL_B', MySourceTable.Source_B
  UNION ALL
  etc, etc
)
  AS lookup(column_name, column_value)

或者也许...

SELECT DISTINCT 'COL_A' AS column_name, Source_A AS column_value FROM MySourceTable
UNION ALL
SELECT DISTINCT 'COL_B' AS column_name, Source_B AS column_value FROM MySourceTable
UNION ALL
etc, etc

Answer 2

您可以使用 row_number()、union all 和聚合来做到这一点：

select max(col_a), max(col_b), . . .
from ((select row_number() over (order by col_a) as seqnum,
              col_a, null as col_b, null as col_c, null as col_d, null as col_e
       from t
       group by col_a
      ) union all
      (select row_number() over (order by col_b) as seqnum,
              null as col_a, col_b, null as col_c, null as col_d, null as col_e
       from t
       group by col_b
      ) union all
      . . .
     ) x
group by seqnum;

Join/Union 不同的列没有重复（Distinct）到一个新的 table

Join/Union different columns without duplicates (Distinct) into a new table

mysql

sql

join

distinct

datatables