比较同一张表上两次选择的结果答案

【问题标题】：compare the result of two selects on same table比较同一张表上两次选择的结果
【发布时间】：2019-06-21 04:45:41
【问题描述】：

假设我有一个表，mytable，如下：

sampleID   rs         A1    A2
--------------------------------
1001       rs123      A     C
1001       rs124      T     C
1001       rs125      A     T
1001       rs126      A     C
1002       rs122      A     C
1002       rs123      T     C
1002       rs124      T     C
1002       rs125      A     C

我想比较任何两个具有共同 rs 值的 sampleID，看看它们的 A1 和/或 A2 值是否匹配。

举个例子

SELECT sampleID as Sample1, rs as rs1, A1 as A1_1, A2 as A2_1 FROM mytable where sampleID = "1001"  

SELECT sampleID as Sample2, rs as rs2, A1 as A1_2, A2 as A2_2 FROM mytable where sampleID = "1002"

如何编写一个 SELECT 语句，获取上述每个 SELECT 的结果，在 rs1 = rs2 处连接，并将 A1_1 与 A1_2 以及 A2_1 与 A2_2 进行比较？

【问题讨论】：

你自己说的有问题。尝试加入same table alias. select t1.samleid as samp1,t2.sampleid as samp2,.....from mytable t1 join mytable t2 on t1. rs = t2.rs2 where ....

标签： mysql select subquery

【解决方案1】：

我会在这里用作自连接来处理比较：

SELECT
    t1.sampleID,
    t2.sampleID,
    t1.rs,
    t1.A1,
    t2.A1,
    (t1.A1 = t2.A1) AS A1_comp,
    t1.A2,
    t2.A2,
    (t1.A2 = t2.A2) AS A2_comp
FROM mytable t1
INNER JOIN mytable t2
    ON t1.sampleID < t2.sampleID
WHERE
    t1.rs = t2.rs
ORDER BY
    t1.sampleID,
    t2.sampleID,
    t1.rs;

Demo

联接条件要求联接左侧的sampleID 严格小于右侧。这确保我们不会重复比较，或将同一样本与其自身进行比较。我们利用 MySQL 语法允许的为 A1 和 A2 值选择布尔等式。别名 A1_comp 和 A1_comp 将是 0 表示不匹配，1 表示匹配。

【讨论】：

【解决方案2】：

为了完整起见，我想包含之前发布的答案的略微修改版本。在此版本中，根据 WHERE 子句仅显示不匹配的 A1/A2 列

SELECT 
A.rs1 as rs, A.Sample1_A1, A.Sample1_A2, B.Sample2_A1, B.Sample2_A2  
    from
    (
    SELECT sampleID as Sample1, rs as rs1, A1 as Sample1_A1, A2 as Sample1_A2 
    FROM mytable where sampleID = "1001" 
    )A left join
    ( 
    SELECT sampleID as Sample2, rs as rs2, A1 as Sample2_A1, A2 as Sample2_A2 
    FROM mytable where sampleID = "1002" 
    )B on A.rs1=B.rs2

where A.Sample1_A1 != B.Sample2_A1 or A.Sample1_A2 != B.Sample2_A2

【讨论】：