使用簡單的SQL查詢從兩個表中選擇數據

Question

如果我有以下查詢

if not exists(select * from DeliveryTemplate where TemplateId=2)
                begin                                       
                    select usersCode, 1,2,'User {UsersCode}',' hello {Username},', null 
                    from User
                end

我如何擴展此查詢，以便從DeliveryTemplate表中再選擇一個列DeliveryCode ？

Answer 1

因此，您需要使用JOIN類的方法：

if not exists(select * from DeliveryTemplate where TemplateId=2)
                begin 
                   select u.usersCode, 1,2,'User {UsersCode}',' hello {Username},', null, dt.DeliveryCode 
                   from User u
                   left join DeliveryTemplate dt on u.Id = dt.UserId
                end

Answer 2

declare @count int
declare @DeliveryCode nvarchar(100)
select @count = count(*), 
       @DeliveryCode = DeliveryCode 
       from DeliveryTemplate 
       where TemplateId=2

if @count = 0 
begin                                       
 select usersCode, 
        1, 
        2,
        'User {UsersCode}', 
        'hello {Username},',
        null,
       @DeliveryCode AS 'DeliveryCode'
       from User
end

Answer 3

應該使用INNER JOIN進行以下操作：

SELECT usersCode, 1,2,'User {UsersCode}',' hello {Username},', null, DeliveryCode
FROM User 
INNER JOIN DeliveryTemplate ON User.ID=DeliveryTemplate.UserId 
WHERE TemplateId=2 

Answer 4

if not exists(select * from DeliveryTemplate where TemplateId=2)
            begin                                       
              select usersCode, 1,2,'User {UsersCode}',' hello {Username},', null, DeliveryCode
              from User AS u
              INNER JOIN DeliveryTemplate AS d
              ON u.ID = d.UserID
            end