Question

我想知道下面的底部3'创建表'段是否有优雅的重构，它会检索相同的结果。我希望能够推广出更大的数据集。非常感谢提前。

    // These top two lines for viewing in SQLite:
    .mode column
    .headers on

    Create table Data_Table (
    Other varchar(255),
    Id varchar(255),
    Value int );

    INSERT INTO Data_Table (other, id, value )
    VALUES ('x','a', 1);

    INSERT INTO Data_Table (other,id, value )
    VALUES ('y','a', 2);

    INSERT INTO Data_Table (other,id, value )
    VALUES ('x','b', 2);

    INSERT INTO Data_Table (other,id, value )
    VALUES ('y','b', 3);

    Create table SubTable_A as 
    select t1.other as other, t1.value as a
    from Data_table as t1 
    where t1.id = 'a';

    Create table SubTable_B as
    select t2.value as b
    from Data_table as t2
    where t2.id = 'b';

    Create table Soln_Table as
    select t1.*, t2.*
    from SubTable_A as t1, SubTable_B as t2
    where t1.rowid = t2.rowid;

底线，我们现在有了这个数据集

    other       a           b         

    ----------  ----------  ----------

    x           1           2         

    y           2           3

Answer 1

您可以使用条件聚合：

select t.other,
       max(case when t.id = 'a' then value end) as a,
       max(case when t.id = 'b' then value end) as b
from Data_Table t
group by t.other;

SQL：将行数据精确翻转到列中

1 个答案: