在一列與所述至少值一組中使用case語句

Question

更換值I有一個表table1

pid_x pid_y count 
    a  b  5 
    a  c  10 
    b  a  20 
    c  e  3 
    d  g  7 
    e  f  10 
    e  b  20 

另外我有一個master_table 它由細節

master_id   pid  price_pid 
    a    a1  10 
    a    b1  20 
    a    c1  30 
    b    d1  40 
    b    e1  50 
    c    f1  60 
    d    g1  70 

在值pid_x等於master_id中的值我想用該最低價格pid替換該pid_x和pid_y，該master_id

即最終結果。

pid_x pid_y count 
    a1  d1  5 
    a1  f1  10 
    d1  a1  20 
    f1  e  3 
    g1  g  7 

等等。

我想爲此案件陳述。

select pidx,pid_y,count from table1 A INNER JOIN master_table m1 ON CASE WHEN A.pid_x = B.master_id then replace that pid_x with cheapest pid dor that mater_id......

Answer 1

我真的希望在MySQL支持的熱膨脹係數，以避免重寫同一個子查詢兩次。但是，試試這個：

SELECT COALESCE(t2.pid, t1.pid_x) pid_x, 
    COALESCE(t3.pid, t1.pid_y) pid_y, 
    SUM(t1.count) COUNT 
FROM table1 t1 
LEFT OUTER JOIN 
    (SELECT t1.* 
    FROM master_table t1 
    INNER JOIN 
    (SELECT master_id, MIN(pid) pid FROM master_table GROUP BY master_id 
    ) t2 
    ON t1.master_id = t2.master_id 
    AND t1.pid  = t2.pid 
) t2 ON t1.pid_x = t2.master_id 
LEFT OUTER JOIN 
    (SELECT t1.* 
    FROM master_table t1 
    INNER JOIN 
    (SELECT master_id, MIN(pid) pid FROM master_table GROUP BY master_id 
    ) t2 
    ON t1.master_id = t2.master_id 
    AND t1.pid  = t2.pid 
) t3 ON t1.pid_x = t3.master_id 
GROUP BY COALESCE(t2.pid, t1.pid_x), 
    COALESCE(t3.pid, t1.pid_y) ;