用PostgreSQL合併表格

Question

這個問題的標題不準確，但我不知道如何總結它。如果可以，請隨時再寫一遍！

下面是兩個表的摘錄：

表table_a

code | year | nb_a 
------+--------+------ 
    A1 | 2017 | 1  
    A2 | 2012 | 2 
    A3 | 2014 | 2 

表table_b

code | year | nb_b 
------+--------+------ 
    A1 | 2013 | 1 
    A1 | 2014 | 1 
    A2 | 2012 | 1 

我需要爲了合併這些表得到這個輸出：

code | year | nb_a | nb_b | total 
------+--------+------+------+------- 
    A1 | 2013 | 0 | 1 |  1 
    A1 | 2014 | 0 | 1 |  1 
    A1 | 2017 | 1 | 0 |  1 
    A2 | 2012 | 2 | 1 |  3 
    A3 | 2014 | 2 | 0 |  2 

我無法找到正確的查詢。我需要像下面（我知道它不會做的工作），但如何獲得在一個表中合併所有代碼和年代碼和幾年不都是兩個表中重複...

SELECT 
    code, 
    "year", 
    table_a.nb_a, 
    table_b.nb_b, 
    table_a.nb_a + table_b.nb_b AS total 

FROM table_a, table_b 
WHERE table_a.code = table_b.code; 

---

下面是SQL腳本快速創建上述表：

CREATE TABLE public.table_a (code TEXT, "year" INTEGER, nb_a INTEGER); 
CREATE TABLE public.table_b (code TEXT, "year" INTEGER, nb_b INTEGER); 

INSERT INTO public.table_a (code, "year", nb_a) VALUES (A1, 2017, 1), (A2, 2012, 2), (A3, 2014, 2); 
INSERT INTO public.table_b (code, "year", nb_b) VALUES (A1, 2013, 1), (A1, 2014, 1), (A2, 2012, 1); 

Answer 1

宇大概是looking爲FULL OUTER JOIN

SELECT 
    coalesce(a.code,b.code), 
    coalesce(a."year",b.year), 
    coalesce(a.nb_a,0), 
    coalesce(b.nb_b,0), 
    coalesce(a.nb_a,0) + coalesce(b.nb_b,0) AS total 
FROM table_a a full outer join table_b b on a.code = b.code and a.year = b.year; 
coalesce | coalesce | coalesce | coalesce | total 
----------+----------+----------+----------+------- 
     1 |  2013 |  0 |  1 |  1 
     1 |  2014 |  0 |  1 |  1 
     1 |  2017 |  1 |  0 |  1 
     2 |  2012 |  2 |  1 |  3 
     3 |  2014 |  2 |  0 |  2 
(5 rows)