Sql 根据两个不同的列选择较大的值

我想选择哪个比率更高，并根据UNION ALL的结果在单个查询结果中输入它。例如，员工200每小时的基本工资为25美元，但他所从事的工作的基本工资为10.00美元。那么他每小时的工资应该是25美元。员工100的基本工资率为10.00，但该职位的基本工资率为25.00。所以他每小时也应该得到25.00分。我想为每位员工选择最高费率。类似于这个想法的东西。从…中选择EmployeeID、费率A或费率B。。。。这是我收集的一些数据

 CREATE Table WageRate(
[ID] [int] IDENTITY(1,1) NOT NULL,
[RateCode] int NULL,
[Rate] Decimal (10,2) NULL
)

INSERT INTO WageRate( RateCode,Rate)
Values (1,10.00), (2,15.00), (3,20.00), (4,25.00)

Create Table Employee(
[ID] [int] IDENTITY(1,1) NOT NULL,
[EmployeeID] int NULL,
[RateCode] int NULL
)

 Insert Into Employee (EmployeeID,RateCode)
 Values (100,1), (200,4)

 Create Table TimeCards(
[ID] [int] IDENTITY(1,1) NOT NULL,
[EmployeeID] int NULL,
[Hours] Decimal (10,2) NULL,
[JobRateCode] int NULL
 )

 Insert Into TimeCards (EmployeeID,[Hours],JobRateCode)
 Values (100,8.00,4), (200,8.00,1)


SELECT t1.Employeeid ,(t0.Rate) as [Rate_A] ,Null FROM WageRate t0 
 INNER JOIN Employee t1 ON t1.RateCode= t0.RateCode
 INNER JOIN TimeCards t2 on t1.EmployeeID = t2.EmployeeID

UNION ALL

SELECT t4.Employeeid ,Null,(t3.Rate) As [Rate_B] FROM WageRate t3 
 INNER JOIN TimeCards t4 on t4.JobRateCode = t3.RateCode
 INNER JOIN Employee t5 ON t4.EmployeeID= t5.EmployeeID

---

使用case表达式，您可以在不使用联合的情况下使用单个查询执行此操作：

SELECT  e.EmployeeID, 
        CASE WHEN ISNULL(ew.Rate, 0.0) > ISNULL(jw.Rate, 0.0) THEN 
            ew.Rate 
        ELSE 
            jw.Rate 
        END As Rate
FROM Employee e
LEFT JOIN TimeCards t On e.EmployeeID = t.EmployeeID
LEFT JOIN WageRate ew ON e.RateCode = ew.RateCode
LEFT JOIN WageRate jw ON t.JobRateCode = jw.RateCode

---

像这样的东西怎么样

 SELECT 
    e.EmployeeID,
    tc.Hours,
    PayRate = CASE WHEN wr1.Rate > wr2.Rate THEN wr1.Rate ELSE wr2.Rate END,
    TotalPay = tc.Hours * CASE WHEN wr1.Rate > wr2.Rate THEN wr1.Rate ELSE wr2.Rate END
 FROM 
    #Employee e
    JOIN #WageRate wr1
        ON e.RateCode = wr1.RateCode
    JOIN #TimeCards tc
        ON e.EmployeeID = tc.EmployeeID
    JOIN #WageRate wr2
        ON tc.JobRateCode = wr2.RateCode;

结果

EmployeeID  Hours                                   PayRate                                 TotalPay
----------- --------------------------------------- --------------------------------------- ---------------------------------------
200         8.00                                    25.00                                   200.0000
100         8.00                                    25.00                                   200.0000

---

要在没有案例逻辑的情况下执行此操作，请执行以下操作：

查询：

SELECT s.EmployeeID, s.Hours, s.jobRate, s.wageRate
  , ( SELECT max(r) FROM (VALUES (s.jobRate),(s.wageRate)) AS value(r)) AS maxRate
FROM (
  SELECT e.EmployeeID, t.Hours
      , COALESCE(w1.Rate,0) AS jobRate
      , COALESCE(w2.Rate,0) AS wageRate
  FROM TimeCards t
  INNER JOIN Employee e ON t.EmployeeID = e.EmployeeID
     LEFT OUTER JOIN WageRate w1 ON e.RateCode = w1.RateCode          
  LEFT OUTER JOIN WageRate w2 ON t.jobRateCode = w2.RateCode
) s
;

| EmployeeID | Hours | jobRate | wageRate | maxRate |
|------------|-------|---------|----------|---------|
|        100 |     8 |      10 |       25 |      25 |
|        200 |     8 |      25 |       10 |      25 |

结果：

SELECT s.EmployeeID, s.Hours, s.jobRate, s.wageRate
  , ( SELECT max(r) FROM (VALUES (s.jobRate),(s.wageRate)) AS value(r)) AS maxRate
FROM (
  SELECT e.EmployeeID, t.Hours
      , COALESCE(w1.Rate,0) AS jobRate
      , COALESCE(w2.Rate,0) AS wageRate
  FROM TimeCards t
  INNER JOIN Employee e ON t.EmployeeID = e.EmployeeID
     LEFT OUTER JOIN WageRate w1 ON e.RateCode = w1.RateCode          
  LEFT OUTER JOIN WageRate w2 ON t.jobRateCode = w2.RateCode
) s
;

| EmployeeID | Hours | jobRate | wageRate | maxRate |
|------------|-------|---------|----------|---------|
|        100 |     8 |      10 |       25 |      25 |
|        200 |     8 |      25 |       10 |      25 |

---

如果不将标识列用作代理键，那么在表中设置标识列有什么意义？我的意思是，如果您的

Employee

表中已经有

EmployeeId

，为什么还要有

ID

列？