Question

嗨我正面临一个问题，我有一种情况需要根据where子句

中匹配列的优先级从db中选择数据

离。我有一张桌子

Employee: FirstName, LastName, City, State.

我想根据标准搜索员工的记录。但情况是，首先我需要获得所有四个标准（列）匹配的记录，然后是所有那些四个标准中的三个（列）匹配的记录，然后是所有那些记录中四个标准中的两个（列）匹配等......

为此，我根据情况创建动态查询，但如果搜索条件会扩展得更多，那么我需要在查询中添加许多条件，因此很难管理动态查询。那么有没有其他方法来处理这个问题？

非常感谢提前。

Answer 1

这已经在SQL Server上进行了测试，但如果它没有立即起作用，应该让你对MySQL有所了解;

测试数据

IF OBJECT_ID('tempdb..#TestData') IS NOT NULL DROP TABLE #TestData
GO
CREATE TABLE #TestData (FirstName varchar(20), LastName varchar(20), City varchar(20), State varchar(20))
INSERT INTO #TestData (FirstName, LastName, City, State)
VALUES
('Jon','Snow','Winterfell','Westeros')
,('Jaime','Lannister','Riverrun','Westeros')
,('Margaery','Tyrell','Kings Landing','Westeros')
,('Cersei','Lannister','Kings Landing','Westeros')
,('Daenerys','Targaryen','Mereen','Essos')
,('Davos','Seaworth','Winterfell','Westeros')
,('Theon','Greyjoy','Mereen','Essos')
,('Tyrion','Lannister','Mereen','Essos')
,('Petyr','Baelish','Winterfell','Westeros')

使用设置为变量的搜索条件进行查询。 case将检查我们拥有的匹配项数以及该字段的order。

DECLARE @Variable1 varchar(20); SET @Variable1 = 'Jon'
DECLARE @Variable2 varchar(20); SET @Variable2 = 'Snow'
DECLARE @Variable3 varchar(20); SET @Variable3 = 'Winterfell'
DECLARE @Variable4 varchar(20); SET @Variable4 = 'Westeros'


SELECT 
FirstName
,LastName
,City
,State
,CASE WHEN FirstName = @Variable1 THEN 1 ELSE 0 END +
 CASE WHEN LastName = @Variable2 THEN 1 ELSE 0 END +
 CASE WHEN City = @Variable3 THEN 1 ELSE 0 END +
 CASE WHEN State = @Variable4 THEN 1 ELSE 0 END Matches

FROM #TestData
ORDER BY (
            CASE WHEN FirstName = @Variable1 THEN 1 ELSE 0 END +
            CASE WHEN LastName = @Variable2 THEN 1 ELSE 0 END +
            CASE WHEN City = @Variable3 THEN 1 ELSE 0 END +
            CASE WHEN State = @Variable4 THEN 1 ELSE 0 END
        ) DESC

结果为：

FirstName   LastName    City            State       Matches
Jon         Snow        Winterfell      Westeros    4
Davos       Seaworth    Winterfell      Westeros    2
Petyr       Baelish     Winterfell      Westeros    2
Jaime       Lannister   Riverrun        Westeros    1
Margaery    Tyrell      Kings Landing   Westeros    1
Cersei      Lannister   Kings Landing   Westeros    1
Daenerys    Targaryen   Mereen          Essos       0
Theon       Greyjoy     Mereen          Essos       0
Tyrion      Lannister   Mereen          Essos       0

Answer 2

您可以使用+1条件对记录进行排名。

http://sqlfiddle.com/#!9/f65790/3

SELECT FirstName, LastName, City, State
FROM Employee
ORDER BY (FirstName = 'John') 
         + (LastName='Snow') 
         + (City='Winterfell') 
         + (State='Nord') DESC

或者如果你需要在某个地方检查那个等级：

SELECT FirstName, LastName, City, State,
        (FirstName = 'John') 
         + (LastName='Snow') 
         + (City='Winterfell') 
         + (State='Nord') Rank
FROM employee
ORDER BY Rank  DESC;

根据where子句中匹配列的优先级从db中选择数据

2 个答案: