如何在SQL中合并两个表？

Question

我有两个桌子：

Table 1 = idhash - username - usermail
Table 2 = idhash - views    - fistseen - lastseen

现在，我想将这些表合并到一个新表中：

Table 3 = idhash - username - usermail - firstseen - lastseen

*请注意，我要删除“视图”列。

我已经尝试过在Google上找到的解决方案，但到目前为止它们似乎没有用。

• 并非表2中的所有idhash列在表1中都有对应的idhash。Stiil用空的用户名和用户邮件存储那些“不匹配”的行

Answer 1

该查询将为您提供结果：

SELECT A.*, B.firstseen, B.lastseen
FROM [Table 1] A
LEFT JOIN [Table 2] B
ON A.idhash = B.idhash

并在[表3]上插入和更新结果：

INSERT INTO [Table 3](idhash, username, usermail, firstseen, lastseen)
SELECT A.*, B.firstseen, B.lastseen
FROM [Table 1] A
LEFT JOIN [Table 2] B
ON A.idhash = B.idhash
LEFT JOIN [Table 3] C
ON A.idhash = C.idhash
WHERE C.idhash IS NULL

-- For SQL Server
UPDATE T3
SET firstseen = T1.firstseen,
    lastseen = T1.lastseen
FROM [Table 3] T3
INNER JOIN (SELECT A.*, B.firstseen, B.lastseen
            FROM [Table 1] A
            LEFT JOIN [Table 2] B
            ON A.idhash = B.idhash) T1
WHERE T3.firstseen != T1.firstseen OR T3.lastseen != T1.lastseen

Answer 2

这是MySQL的解决方案：

CREATE TABLE table3
// First get all the rows from table2, paired with matching rows from table1
(SELECT a.idhash, b.username, b.usermail, a.firstseen, a.lastseen
FROM table2 a
LEFT JOIN table1 b
  ON b.idhash = a.idhash)
// Now get the remaining rows from table1 that don't have matches
UNION ALL
(SELECT null, a.username, a.usermail, null, null
FROM table1 a
LEFT JOIN table2 b
  ON b.idhash = a.idhash
WHERE b.idhash IS NULL)

如果您不希望table1中的行在table2中没有对应的行，则删除UNION子句中的第二个查询。

Answer 3

您可以选择编程语言来强行使用它。 只需构建一个新表，查询两个表，以编程方式联接行，但是需要将它们联接起来，插入新表中。

Answer 4

insert into table3
select t1.idhash, t1.username, t1.usermail, t2.firstseen,t2.lastseen
from table1 t1 left join table2 t2 on t1.idhas=t2.idhas

Answer 5

这应该是一个好的开始。 您需要告诉我们如何处理不匹配的记录，然后我们才能提供更具体的信息。

Select 
    table1.idhash
    ,username
    ,usermail
    ,firstseen
    ,lastseen
From table1
    left join table2
      on table1.idhash = table2.idhash

Answer 6

使用create语句中的字段类型创建新表

http://www.w3schools.com/sql/sql_create_table.asp

然后insert Into Table3 <yourtable> select a.f1,b.f2,c.f3 from Table1 a, Table 2 b on a.id = b.id

Answer 7

这非常接近蛮力。

select coalesce(t1.idhash, t2.idhash) as idhash
, username
, usermail
, firstseen
, lastseen
into table3
from table1 t1
cross join table2 t2

Answer 8

尝试这个：

INSERT INTO table3 (idhash, username, usermail, firstseen, lastseen)
SELECT  a.idhash, a.username, a.usermail,
        b.firstseen, b.lastseen
FROM    table1 a LEFT JOIN table2 b 
            ON a.idhash = b.idhash

Answer 9

我会这样做：

           CREATE TABLE table3
                     AS
                 SELECT idhash, username, usermail, firstseen, lastseen
                   FROM Table1
NATURAL FULL OUTER JOIN Table2