使用 SQL 在具有重复数据的表之间插入

Question

My data is structured as follows:

Table 1 - Employee</b>

-ID
-Name
-Address
-City
-State
...

Table 2 - Audit

-Address
-City
-State
...

I need to from the employee table matching the from the smaller audit table with address information from the larger employee table (with the assumption that no employees share an address)

Here is the code I have been working with, the query generates the data that I want, but the update, set sequence fails with the following message:

Msg 512, Level 16, State 1, Line 1 Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.

UPDATE AuditTable SET employee_id = (
    SELECT e.employee_id 
    FROM EmployeeTable e 
    JOIN AuditTable a
        ON  e.address = a.address
        AND e.home_city = a.home_city
        AND e.home_st = a.home_st
)

The same employee needs to be able to repeat multiple times within the audit table and still show the same id, which is causing my problems. I already tried substituting for and using in my select statement but had no luck getting what I needed.

Answer 1

The problem with your query is that the subquery is not correlated with the table being updated, hence it generates multiple records.

If there are no duplicates for (address, home_city, home_st) tuples in the Employee table, then you can use a simple correlated subquery:

UPDATE AuditTable SET employee_id = (
    SELECT e.employee_id 
    FROM EmployeeTable e 
    WHERE 
        e.address = AuditTable.address 
        AND e.home_city = AuditTable.home_city 
        AND e.home_st = AuditTable.home_st
)

If duplicates may happen, then you can use TOP 1 or an aggregate function such as MAX() :

UPDATE AuditTable SET employee_id = (
    SELECT TOP 1 e.employee_id 
    FROM EmployeeTable e 
    WHERE 
        e.address = AuditTable.address 
        AND e.home_city = AuditTable.home_city 
        AND e.home_st = AuditTable.home_st
)

Answer 2

Use a join:

UPDATE a
SET a.employee_id = e.employee_id
FROM AuditTable a INNER JOIN EmployeeTable e 
ON e.address = a.address AND e.home_city = a.home_city AND e.home_st = a.home_st