防止 SQL“FOR JSON”导致重复答案

【问题标题】：Prevent SQL "FOR JSON" from causing duplication防止 SQL“FOR JSON”导致重复
【发布时间】：2017-07-03 00:20:51
【问题描述】：

我有一个主表 Departments。详细信息表员工具有指向部门表的外键。当使用 PATH 选项将简单连接查询作为 JSON 返回时，它会为部门列出多行。而当使用 AUTO 选项时，它会返回唯一的部门，但我失去了对模式的控制。我怎样才能使用 PATH 选项，并且仍然能够像 AUTO 选项一样返回唯一部门。代码如下：

Declare @Departments as table (DeptName varchar(100), Location varchar(100) )
insert @Departments 
select 'IT', 'San Francisco'
union
select 'Sales', 'Miami'
union
select 'Finance', 'NYC'

Declare @Employees as table (DeptName varchar(100) , EmployeeName varchar(100), Salary Decimal(7,2))
insert @Employees 
select 'Finance', 'Ponzi', 1000
union
select 'Finance', 'Madoff', 10000
union
select 'IT' , 'Bill', 20000
union
select 'IT', 'Steve', 100

select D.DeptName [Department.Name], D.Location [Department.Location], E.EmployeeName [Employee.Name], E.Salary [Employee.Salary]
from
    @Departments D
    left join @Employees E on E.DeptName = D.DeptName
for JSON Auto

自动模式返回以下结果。注意每个部门只出现一次：

[{
        "Department.Name": "Finance",
        "Department.Location": "NYC",
        "E": [{
                "Employee.Name": "Madoff",
                "Employee.Salary": 10000.00
            }, {
                "Employee.Name": "Ponzi",
                "Employee.Salary": 1000.00
            }
        ]
    }, {
        "Department.Name": "IT",
        "Department.Location": "San Francisco",
        "E": [{
                "Employee.Name": "Bill",
                "Employee.Salary": 20000.00
            }, {
                "Employee.Name": "Steve",
                "Employee.Salary": 100.00
            }
        ]
    }, {
        "Department.Name": "Sales",
        "Department.Location": "Miami",
        "E": [{}
        ]
    }
]

PATH 选项返回以下结果。注意每个部门的多次出现：

[{
        "Department": {
            "Name": "Finance",
            "Location": "NYC"
        },
        "Employee": {
            "Name": "Madoff",
            "Salary": 10000.00
        }
    }, {
        "Department": {
            "Name": "Finance",
            "Location": "NYC"
        },
        "Employee": {
            "Name": "Ponzi",
            "Salary": 1000.00
        }
    }, {
        "Department": {
            "Name": "IT",
            "Location": "San Francisco"
        },
        "Employee": {
            "Name": "Bill",
            "Salary": 20000.00
        }
    }, {
        "Department": {
            "Name": "IT",
            "Location": "San Francisco"
        },
        "Employee": {
            "Name": "Steve",
            "Salary": 100.00
        }
    }, {
        "Department": {
            "Name": "Sales",
            "Location": "Miami"
        }
    }
]

使用PATH模式如何防止部门多次出现？

【问题讨论】：

标签： sql-server json path sql-server-2016

【解决方案1】：

没关系。必须先通过 JSON 化员工表来修改源查询，然后与部门表交叉应用，最后再对整个事情进行 JSON 化。

查询：

Declare @Departments as table (DeptName varchar(100), Location varchar(100) )
insert @Departments 
select 'IT', 'San Francisco'
union
select 'Sales', 'Miami'
union
select 'Finance', 'NYC'

Declare @Employees as table (DeptName varchar(100) , EmployeeName varchar(100), Salary Decimal(7,2))
insert @Employees 
select 'Finance', 'Ponzi', 1000
union
select 'Finance', 'Madoff', 10000
union
select 'IT' , 'Bill', 20000
union
select 'IT', 'Steve', 100

select D.DeptName [Department.Name], D.Location [Department.Location], jsonEmployees.Employees
from
    @Departments D
    cross apply (
        select EmployeeName [Employee.Name], Salary [Employee.Salary]
        from @Employees Employee 
        where Employee.DeptName = D.DeptName 
        For JSON path
    ) JsonEmployees(Employees)

for JSON path

结果：

[{
        "Department": {
            "Name": "Finance",
            "Location": "NYC"
        },
        "Employees": [{
                "Employee": {
                    "Name": "Madoff",
                    "Salary": 10000.00
                }
            }, {
                "Employee": {
                    "Name": "Ponzi",
                    "Salary": 1000.00
                }
            }
        ]
    }, {
        "Department": {
            "Name": "IT",
            "Location": "San Francisco"
        },
        "Employees": [{
                "Employee": {
                    "Name": "Bill",
                    "Salary": 20000.00
                }
            }, {
                "Employee": {
                    "Name": "Steve",
                    "Salary": 100.00
                }
            }
        ]
    }, {
        "Department": {
            "Name": "Sales",
            "Location": "Miami"
        }
    }
]

【讨论】：