如何从多个 select 语句创建 SQL 查询结果（没有 UNION）

Question

我有一些选择语句，当单独执行时会返回我需要的内容。 我想将所有这些选择语句组合成一个看起来像普通表格的表格。 我尝试了 UNION 但得到一个错误，说我需要相同数量的参数（显然是列字段），但这不是我想要的。 所以我尝试了这个（我的代码到目前为止）

SELECT Company_Code FROM Company
UNION
SELECT Founder FROM Company
UNION
SELECT CAST(COUNT(Company.id) as varchar(5)) as Number_of_LeadManagers
FROM Lead_Manager
LEFT JOIN Company
ON (Lead_Manager.Companyid = Company.id)
GROUP BY Company.id
UNION
SELECT COUNT(Company.id) as Number_of_SeniorManagers
FROM Senior_Manager
LEFT JOIN Company
ON (Senior_Manager.Companyid = Company.id)
GROUP BY Company.id
UNION
SELECT COUNT(Company.id) as Number_of_Managers
FROM Manager
LEFT JOIN Company
ON (Manager.Companyid = Company.id)
GROUP BY Company.id
UNION
SELECT COUNT(Company.id) as Number_of_Employees
FROM Employee
LEFT JOIN Company
ON (Employee.Companyid = Company.id)
GROUP BY Company.id

整个语句返回我想要的所有内容。 如果每个 select 语句单独运行，则获取我的代码，它会返回我想要的内容（总是返回两行） 我想要的是最终结果只需将所有这些选择语句结果放在一起，这样这将显示 2 行，无论选择语句返回多少列。

我想要澄清的想法 如果我执行

SELECT Company_Code,Founder FROM Company

我明白了

**Result1**
row 1 :  C1 Monika
row 2 :  C2 Samantha

（总是只有 2 行） 如果我执行

   SELECT CAST(COUNT(Company.id) as varchar(5)) as Number_of_LeadManagers
    FROM Lead_Manager
    LEFT JOIN Company
    ON (Lead_Manager.Companyid = Company.id)
    GROUP BY Company.id

我明白了

**Result2**
row 1 : 1
row 2 : 1

其他选择语句基本相同，只是使用不同的表进行计数。 我想要的只是一个允许我将 Result1 和 Result2 放在一起的查询（以及其余的选择结果） 期望的最终结果

**Result3**
row 1 : C1 Monika 1
row 2 : C2 Samantha 1

PS.上周开始的 SQL 还在苦苦挣扎，顺便说一下这是一个家庭作业项目。 如果我的思维方式是错误的，请告诉我，但这就是我在大脑中的看法，无法完全弄清楚如何使用 SQL ;P

Answer 1

如果你有一个字符串列，那么你需要为 union c 中的每个选择提供一个字符串列

所以你只需要像第一次选择一样将每个计数转换为 char

SELECT Company_Code FROM Company
UNION
SELECT Founder FROM Company
UNION
SELECT CAST(COUNT(Company.id) as varchar(5)) as Number_of_LeadManagers
FROM Lead_Manager
LEFT JOIN Company
ON (Lead_Manager.Companyid = Company.id)
GROUP BY Company.id
UNION
SELECT CAST(COUNT(Company.id) as varchar(5)) as Number_of_SeniorManagers
FROM Senior_Manager
LEFT JOIN Company
ON (Senior_Manager.Companyid = Company.id)
GROUP BY Company.id
UNION
SELECT CAST(COUNT(Company.id)  as varchar(5)) as Number_of_Managers
FROM Manager
LEFT JOIN Company
ON (Manager.Companyid = Company.id)
GROUP BY Company.id
UNION
SELECT CAST(COUNT(Company.id) as varchar(5)) as Number_of_Employees
FROM Employee
LEFT JOIN Company
ON (Employee.Companyid = Company.id)
GROUP BY Company.id

但如果您需要同一行上的所有结果，您可以在子查询上使用左连接

SELECT Company_Code , Founder
  , t1.Number_of_LeadManagers
  , t2.Number_of_SeniorManagers
  , t3.Number_of_Managers 
  , t4.Number_of_Employees
FROM Company
LEFT JOIN (
SELECT Company.id, COUNT(Company.id) as Number_of_LeadManagers
FROM Lead_Manager
LEFT JOIN Company ON Lead_Manager.Companyid = Company.id
GROUP BY Company.id
) t1 on t1.id = company.id
LEFT JOIN (
SELECT  company.id, COUNT(Company.id)  as Number_of_SeniorManagers
FROM Senior_Manager
LEFT JOIN Company
ON (Senior_Manager.Companyid = Company.id)
GROUP BY Company.id
) t2 ON t2.id = company.id
LEFT JOIN (
SELECT company.id, COUNT(Company.id) as Number_of_Managers
FROM Manager
LEFT JOIN Company
ON (Manager.Companyid = Company.id)
GROUP BY Company.id
) t3 ON t3.id = company.id
LEFT JOIN (
SELECT company.id, COUNT(Company.id) as Number_of_Employees
FROM Employee
LEFT JOIN Company
ON (Employee.Companyid = Company.id)
GROUP BY Company.id
) t4 ON t4.id = company.id

Answer 2

将它们全部放在同一行上的最简单方法就是使用相关子查询。

SELECT Company.Company_Code, Company.Founder 
  , (
        SELECT COUNT(Company.id) 
        FROM Lead_Manager
        WHERE Lead_Manager.Companyid = Company.id
    ) AS Number_of_LeadManagers
  , (
        SELECT COUNT(Company.id) 
        FROM Senior_Manager
        WHERE Senior_Manager.Companyid = Company.id
    ) AS Number_of_SeniorManagers
  , (
        SELECT COUNT(Company.id) 
        FROM Manager
        WHERE Manager.Companyid = Company.id
    ) AS Number_of_Managers
  , (
        SELECT COUNT(Company.id) 
        FROM Employee
        WHERE Employee.Companyid = Company.id
    ) AS Number_of_Employees
FROM Company

根据您的数据，您可能需要进一步消除重复数据。