如何使用Guava连接两个表

Question

Fact table :

Id Year Month countryId Sales
1  1999 1     1         3000
2  1999 2     1         2300
3  2000 3     2         3999
4  2000 4     3         2939

Dimension table:

Id country province
1  US      LA
2  US      CA
3  US      GA
4  EN      LN

and I use Guava table like this :

Table<Integer, String, Object> table = Tables.newCustomTable(
        Maps.<Integer, Map<String, Object>> newLinkedHashMap(),
        new Supplier<Map<String, Object>>() {
            public Map<String, Object> get() {
                return Maps.newLinkedHashMap();
            }
        });

    table.put(1, "Year", 1999);
    table.put(1, "Month", 1);
    table.put(1, "countyId", 1);
    table.put(1, "Sales", 3000);
    // ...... etc


    table1.put(1, "county", "US");
    table1.put(1, "provice", 1999);
    // ......

I want to implement a LEFT JOIN like:

1 1999 1 1 3000 US LA
2 1999 2 1 2300 US LA
3 2000 3 2 3999 US CA
4 2000 4 3 2939 EN LN

What should I do?

Answer 1

Guava's Table isn't supposed to be used like any SQL's table, as it is a collection. SQL's tables are designed to be indexable, sortable, filterable, etc. Guava's Table has only a fraction of those and only indirectly, and joints aren't part of them (unless you play with transformations).

What you need to do is to have your two tables and loop through the elements of table and find the corresponding mapping in table1 .

In your case, I believe you're better off with a List replacing table and a Guava Table for table1 . Loop through the list and make your final objects as you get your elements.