SQL查询从键表中选择多个条目到同一行的不同列中

Question

我正在尝试创建一个 SQL 查询，它可以从表中选择多个条目并将这些条目输入到同一行的不同列中。

例子：

表1“人”

|---------------------|------------------|------------------|
|      PersonID       |     FirstName    |     LastName     |
|---------------------|------------------|------------------|
|          1          |      John        |     Smith        |
|---------------------|------------------|------------------|
|          2          |      Jane        |     Doe          |
|---------------------|------------------|------------------|

表 2“电话类型”

|---------------------|------------------|
|      PhoneTypeID    |     Name         |
|---------------------|------------------|
|          1          |      Home        |
|---------------------|------------------|
|          2          |      Work        |
|---------------------|------------------|
|          3          |      Mobile      |
|---------------------|------------------|

表 3“电话号码”

|---------------------|------------------|------------------|
|      PersonID       |     PhoneTypeID  |     PhoneNumber  |
|---------------------|------------------|------------------|
|          1          |      1           |     12300        |
|---------------------|------------------|------------------|
|          2          |      1           |     45600        |
|---------------------|------------------|------------------|
|          2          |      2           |     78900        |
|---------------------|------------------|------------------|

SQL 查询的预期结果：

|------------------|---------------|---------------|---------------|
|      FirstName   |  LastName     |HomePhoneNumber|WorkPhoneNumber|
|------------------|---------------|---------------|---------------|
|      John        |  Smith        |  12300        |  NULL         |
|------------------|---------------|---------------|---------------|
|      Jane        |  Doe          |  45600        |  78900        |
|------------------|---------------|---------------|---------------|

我想从 PhoneNumber 表中选择家庭和工作电话号码，并将它们写在同一行的不同列中。

查询应该看起来像这样：

SELECT Person.FirstName, Person.LastName, PhoneNumber.PhoneNumber AS HomePhoneNumber, PhoneNumber.PhoneNumber AS WorkPhoneNumber
FROM Person
LEFT OUTER JOIN PhoneNumber ON Person.PersonID = PhoneNumber.PersonID
LEFT OUTER JOIN PhoneType ON PhoneType.PhoneTypeID = PhoneNumber.PhoneTypeID
WHERE PhoneType.PhoneTypeID = 'Home'
OR PhoneType.PhoneTypeID = 'Work'

Answer 1

您可以在 join 子句中指定 PhoneTypeID

SELECT Person.FirstName, Person.LastName, HomePhone.PhoneNumber AS HomePhoneNumber, WorkPhone.PhoneNumber AS WorkPhoneNumber
FROM Person
LEFT OUTER JOIN PhoneNumber HomePhone ON Person.PersonID = HomePhone.PersonID
    and HomePhone.PhoneTypeID = 1
LEFT OUTER JOIN PhoneNumber WorkPhone ON Person.PersonID = WorkPhone.PersonID
    and WorkPhone.PhoneTypeID = 2

http://sqlfiddle.com/#!9/9cf19c2/1

Answer 2

你可以使用correlated subquery作为

select FirstName,LastName,
       ( select PhoneNumber  
           from PhoneNumber  
          where PhoneTypeID = 1 and PersonID = p.PersonID ) as  HomePhoneNumber, 
       ( select PhoneNumber 
           from PhoneNumber  
          where PhoneTypeID = 2 and PersonID = p.PersonID ) as  WorkPhoneNumber
   from person p;

或将conditional aggregation 与left join 一起使用

select FirstName,LastName, 
       max( case when PhoneTypeID = 1 then n.PhoneNumber end  ) as  HomePhoneNumber, 
       max( case when PhoneTypeID = 2 then n.PhoneNumber end  ) as  WorkPhoneNumber
   from person p
   left join PhoneNumber n 
     on n.PersonID = p.PersonID
  group by FirstName,LastName 

Demo