Question

I’m left joining 2 tables (table1 and table2).

The 1st table contains unique globalcid of each record, 2nd table contains multiple occurrences of the same globalcid. Note: globalcid is the reference field of table2 to table1.

table1

globalcid  / itemdesc
1          / item 1
2          / item 2
3          / item 3
4          / item 4
5          / item 5

table2

globalcid    /  recordcid
1            / 1
1            / 2
2            / 1
3            / 1
3            / 2
3            / 3
5            / 1

I want a query to return only the records from [table1] with record in [table2] GROUP BY table2.globalcid but will return last record of each globalcid

In the example above it should return

globalcid  / itemdesc  / table2.globalcid
1          / item 1    / 2
2          / item 2    / 1
3          / item 3    / 3
5          / item 5    / 1

Answer 1

SELECT 
    a.*,
    MAX(b.recordcid) AS maxcid
FROM 
    table1 a
INNER JOIN 
    table2 b ON a.globalcid = b.globalcid
GROUP BY 
    a.globalcid

If you’re only concerned about the recordcid and do not need any other columns from that table, then this should be fine. However, if there are other columns in the table like such:

globalcid    /  recordcid   /  othercolumn 
------------------------------------------
1            / 1            /  bertrand
1            / 2            /  centipede
2            / 1            /  yarn
3            / 1            /  obviate
3            / 2            /  hyper
3            / 3            /  fish
5            / 1            /  larry

…then the MAX() value will not line up with its corresponding row data in othercolumn, and instead you must wrap the selection of the max in a subselect like so:

SELECT
    a.*,
    c.recordcid,
    c.othercolumn
FROM
    table1 a
INNER JOIN
    (
        SELECT globalcid, MAX(recordcid) AS maxcid
        FROM table2
        GROUP BY globalcid
    ) b ON a.globalcid = b.globalcid
INNER JOIN
    table2 c ON b.globalcid = c.globalcid AND b.maxcid = c.recordcid

Resulting in:

globalcid    /  itemdesc    /  recordcid   /  othercolumn 
---------------------------------------------------------
1            /  item1       / 2            /  centipede
2            /  item2       / 1            /  yarn
3            /  item3       / 3            /  fish
5            /  item5       / 1            /  larry