How to update tables from an external Access database with identical tables? - sql

Question

Using MS Access, via VBA, I have been trying to update an main Access database table from an identically structured external Access database table. Same columns, same fields. The external databases are used to update a central main database.
What I have been trying to develop is a line of SQL that only appends the entries that are completely unique. Because there is no foreign keys or unique identifiers for the incoming data that can be referenced, I am required to check each field to make sure that there are no exact duplicates. So, if the table had 2 fields, if entries failed the logic test
intTable.field1 = extTable.field1 And intTable.field2 = extTable.field2
then those are the entries that would be appended.
The code I came up with is below, and when it runs it tries to append (in a Gary Oldman voice) EVERYTHING. I can't find out what could be wrong with it, as it's almost like it ignores the WHERE or WHERE NOT EXIST. I have tried dozens of small edits and alternate versions. Either is appends all or none.
INSERT INTO Table1
SELECT field1, field2, field3, field4, field5
FROM [;DATABASE=C:\extDB.accdb].[Table1] sourceDB
WHERE NOT EXISTS (SELECT *
FROM [;DATABASE=C:\extDB.accdb].[Table1] sourceDB1
WHERE ('Table1.[field1]'='sourceDB1.[field1]' And
'Table1.[field2]'='sourceDB1.[field2]' And
'Table1.[field3]'='sourceDB1.[field3]' And
'Table1.[field4]'='sourceDB1.[field4]' And
'Table1.[field5]'='sourceDB1.[field5]'));
FINAL CODE (after implementing ArcherBird's solution):
INSERT INTO Table1
SELECT field1, field2, field3, field4, field5
FROM [;DATABASE=C:\extDB.accdb].[Table1] sourceDB
WHERE NOT EXISTS (SELECT *
FROM [;DATABASE=C:\extDB.accdb].[Table1] sourceDB1
WHERE ((sourceDB.[field1] = sourceDB1.[field1] Or (sourceDB.[field1] IS NULL And sourceDB1.[field1] IS NULL)) And
(sourceDB.[field2] = sourceDB1.[field2] Or (sourceDB.[field2] IS NULL And sourceDB1.[field2] IS NULL)) And
(sourceDB.[field3] = sourceDB1.[field3] Or (sourceDB.[field3] IS NULL And sourceDB1.[field3] IS NULL)) And
(sourceDB.[field4] = sourceDB1.[field4] Or (sourceDB.[field4] IS NULL And sourceDB1.[field4] IS NULL)) And
(sourceDB.[field5] = sourceDB1.[field5] Or (sourceDB.[field5] IS NULL And sourceDB1.[field5] IS NULL)) ));

Answer 1

1) Remove the string quotes from your field comparison logic.
2) You have aliased Table1 in your query as sourceDB, so use that reference.
3) The table where you check for non-existence ought to be the "local" version of Table1 (the one you are inserting into).
INSERT INTO Table1
SELECT field1,
field2,
field3,
field4,
field5
FROM [;DATABASE=C:\extDB.accdb].[Table1] sourceDB
WHERE NOT EXISTS (SELECT *
FROM [Table1] sourceDB1
WHERE (sourceDB.[field1] = sourceDB1.[field1] And
sourceDB.[field2] = sourceDB1.[field2] And
sourceDB.[field3] = sourceDB1.[field3] And
sourceDB.[field4] = sourceDB1.[field4] And
sourceDB.[field5] = sourceDB1.[field5]));
EDIT:
To deal with the case where these fields might have null values, you cannot do a simple = comparison since null does not equal null. The best way I can think of to get around this in MS Access would be to replace null with some other value that is not likely to be used. In doing so, you also need to make sure you chose replacement values that are consistent with the data type. I will make an assumption that all your fields are text.
INSERT INTO Table1
SELECT field1,
field2,
field3,
field4,
field5
FROM [;DATABASE=C:\extDB.accdb].[Table1] sourceDB
WHERE NOT EXISTS (SELECT *
FROM [Table1] sourceDB1
WHERE (nz(sourceDB.[field1],"!##") = nz(sourceDB1.[field1],"!##") And
nz(sourceDB.[field2],"!##") = nz(sourceDB1.[field2],"!##") And
nz(sourceDB.[field3],"!##") = nz(sourceDB1.[field3],"!##") And
nz(sourceDB.[field4],"!##") = nz(sourceDB1.[field4],"!##") And
nz(sourceDB.[field5],"!##") = nz(sourceDB1.[field5],"!##")));