在mysql中如何打印如下：只在一个查询中

Question

我有一张员工桌

而我想要的是薪水<6000转换成一列，薪水> 6000转换成另一张表......就像这样

我试试这个：没有产生正确的结果

SELECT 
    (CASE WHEN salary <  6000 THEN salary END) salary_less_then_6000, 
    (CASE WHEN salary >  6000 THEN salary END) salary_gerater_then_6000 
FROM employee

希望你明白我的意思。任何帮助都是值得的

Answer 1

实现这一目标的方法是创建两个表，一个工资<6000，另一个工资> = 6000，然后JOIN。现在由于这些表中没有自然排序，我们必须为每个表创建一个人工行号，然后根据它创建JOIN。由于我们不知道哪个表可能有更多行，我们必须做一个FULL OUTER JOIN。不幸的是，MySQL不支持这一点，因此我们必须使用带有LEFT JOIN的UNION RIGHT JOIN来模拟它：

SELECT e1.salary AS salary_less_then_6000, e2.salary AS salary_greater_then_6000 
FROM (SELECT salary, @rownum1:=@rownum1+1 AS rownum
      FROM employees
      JOIN (SELECT @rownum1 := 0) r
      WHERE salary < 6000
      ORDER BY salary
      ) e1
LEFT JOIN (SELECT salary, @rownum2:=@rownum2+1 AS rownum
      FROM employees
      JOIN (SELECT @rownum2 := 0) r
      WHERE salary >= 6000
      ORDER BY salary
      ) e2
ON e1.rownum = e2.rownum
UNION
SELECT e1.salary AS salary_less_then_6000, e2.salary AS salary_greater_then_6000 
FROM (SELECT salary, @rownum3:=@rownum3+1 AS rownum
      FROM employees
      JOIN (SELECT @rownum3 := 0) r
      WHERE salary < 6000
      ORDER BY salary
      ) e1
RIGHT JOIN (SELECT salary, @rownum4:=@rownum4+1 AS rownum
      FROM employees
      JOIN (SELECT @rownum4 := 0) r
      WHERE salary >= 6000
      ORDER BY salary
      ) e2
ON e1.rownum = e2.rownum

输出（来自我的演示）

salary_less_then_6000   salary_greater_then_6000
3000                    7000
5000                    8000
(null)                  9000

SQLFiddle Demo