Greetings, As mentioned in the PostgreSQL Weekly News, SQL2003 has been approved. Looking at one of the recent drafts it appears that MERGE has been added to the spec. MERGE is described as "Conditionally update rows of a table, or insert new rows into a table, or both." Support for this has been asked for in the past and if anything demand for this has increased. Is anyone working on this? Is there any status on it?
Additionally, from the draft I'm reading the SQL2003 standard makes MERGE very capable but without obvious defaults for the simple case. While I believe support for the standard should be paramount it would make a great deal of sense to allow simple operations without unnecessary complexity. For example: Table T1 exists with columns a, b, c where a, b is the primary key. T1 contains a single tuple '1, 2, 3'. I would now like to either update or insert the primary key '1, 2' with the value '4'. From what I understand of the specification this would be done by: a) insert into T2 values (1,2,4); merge into T1 USING T2 ON T1.a=T2.a and T1.b=T2.b WHEN MATCHED THEN UPDATE SET T1.c = T2.c ON T1.a=T2.a and T1.b=T2.b WHEN NOT MATCHED THEN INSERT (a,b,c) VALUES (T2.a,T2.b,T2.c); This requires an addtional table (T2). There may be a better way around this but I know that PostgreSQL already allows select statements without a from clause, so this could be simplified to: b) merge into T1 USING (select 1 as a, 2 as b, 4 as c) as T2 ON T1.a=T2.a and T1.b=T2.b WHEN MATCHED THEN UPDATE SET T1.c = T2.c ON T1.a=T2.a and T1.b=T2.b WHEN NOT MATCHED THEN INSERT (a,b,c) VALUES (T2.a,T2.b,T2.c); Still pretty long-winded for what most would consider a relatively simple request. My goal would be the ability to have implied ON/WHEN clauses and USING VALUES, like so: c) merge into T1 USING VALUES (1,2,4); The ON clauses are implied primary key matches. The WHEN clause for MATCHED is then to UPDATE SET all columns which are not part of the primary key. The WHEN clause for NOT MATCHED is to INSERT the row. Clearly this last usage is what I would prefer for this case. It also parallels the 'replace into' which MySQL has which would make migration from MySQL to PostgreSQL much easier for programs and users. Please let me know if there's something I'm missing in the specification that would allow for a simple case similar to what I've illustrated, either with MERGE or without. Of course, the expectation is that MERGE wouldn't be able to fail because of another instance adding a row with the same primary key. I plan to forward this suggestion on to the SQL committee as well, though I don't know what kind of response, if any, I'll get. Feel free to address the standard MERGE support seperately from my suggestion. I have need for both and so both are of interest and do not have to come at the same time. Many thanks, Stephen
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