Access两张共享Machine Name/RAM字段的表合并补全RAM数据需求

Alright, let's figure out how to merge those two Access tables and fill in as many missing RAM values as possible. Here's a practical, step-by-step solution that should get you exactly what you need:

Access doesn’t natively support FULL OUTER JOIN, so we’ll use a combination of LEFT JOIN and UNION to cover all machines from both tables, while prioritizing non-empty RAM values.

First, create a select query with this SQL:

-- Get all machines from Table1, use Table2's RAM if Table1's is empty
SELECT 
    t1.[Machine Name],
    Nz(t1.RAM, t2.RAM) AS RAM
FROM 
    Table1 t1
LEFT JOIN 
    Table2 t2 ON t1.[Machine Name] = t2.[Machine Name]

UNION

-- Add machines that only exist in Table2
SELECT 
    t2.[Machine Name],
    t2.RAM
FROM 
    Table2 t2
LEFT JOIN 
    Table1 t1 ON t2.[Machine Name] = t1.[Machine Name]
WHERE 
    t1.[Machine Name] IS NULL

• The Nz function here does the heavy lifting: if Table1’s RAM is empty, it pulls the RAM value from Table2 instead.
• The UNION ensures we don’t miss any machines that only appear in Table2.

If a machine has multiple entries in either table, we’ll group them to keep only one record per machine, retaining the first non-empty RAM value. Wrap the previous query in a grouping query:

SELECT 
    [Machine Name],
    First(Nz(RAM, NULL)) AS RAM
FROM (
    -- Paste the entire UNION query from Step 1 here
    SELECT 
        t1.[Machine Name],
        Nz(t1.RAM, t2.RAM) AS RAM
    FROM 
        Table1 t1
    LEFT JOIN 
        Table2 t2 ON t1.[Machine Name] = t2.[Machine Name]

    UNION

    SELECT 
        t2.[Machine Name],
        t2.RAM
    FROM 
        Table2 t2
    LEFT JOIN 
        Table1 t1 ON t2.[Machine Name] = t1.[Machine Name]
    WHERE 
        t1.[Machine Name] IS NULL
) AS CombinedData
GROUP BY [Machine Name]

• If you suspect conflicting RAM values for the same machine (e.g., different entries show 8GB and 16GB), replace First with Max or Min to pick a consistent value—just make sure it makes sense for your data.

Once you’ve verified the query returns the right results (run it first to check!), convert it to a make-table query:

1. In Access’s query design view, go to the Query Type menu and select Make-Table Query.
2. Name your new table (e.g., CombinedMachineSpecs) and click OK.
3. Run the query—Access will create the new table with all merged, cleaned data.

• If a machine has empty RAM in both tables, we can’t magic up a value—those will stay empty, but this approach minimizes that as much as possible.
• Always back up your original tables before running make-table queries, just in case you need to revert!

内容的提问来源于stack exchange，提问作者Storm2508