Mysql 如何在SQL中合并两个表？

我有两张桌子：

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：

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

*请注意，我想删除“视图”列

我尝试过在谷歌上找到的解决方案，但到目前为止，它们似乎不起作用

• 并非表2中的所有idhash列在表1中都有相应的idhash。仍然使用空用户名和usermail存储那些“不匹配”的行

---

您可以选择编程语言对其进行强制。只需构建一个新表，查询两个表，以编程方式连接需要连接的行，插入到新表中。

您可以选择编程语言强制执行。只需构建一个新表，查询两个表，以编程方式连接需要连接的行，插入到新表中。

此查询将提供以下结果：

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

并在[表3]中插入和更新结果：

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

---

此查询将为您提供以下结果：

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

并在[表3]中插入和更新结果：

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

---

这应该是一个好的开始。在我们提供更具体的信息之前，您需要告诉我们如何处理不匹配的记录

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

---

这应该是一个好的开始。在我们提供更具体的信息之前，您需要告诉我们如何处理不匹配的记录

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

---

使用Create语句中的字段类型创建新表

---

然后在表3中插入一个

，在a.id=b.id上从表1 a、表2 b中选择a.f1、b.f2、c.f3，用Create语句中的字段类型创建新表


然后在表3中插入一个
，在a.id=b.id上从表1a、表2b中选择a.f1、b.f2、c.f3，这非常接近暴力

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

这是非常接近暴力的

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

试试这个：

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

试试这个：

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

我会这样做：

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

我会这样做：

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

以下是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)

如果不希望表1中的行在表2中没有对应的行，请删除
UNION
子句中的第二个查询。
以下是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)

如果不希望表1中的行在表2中没有对应的行，请删除
UNION
子句中的第二个查询。
您使用的是什么数据库服务器？为了澄清，您是说表2中的行在表1中没有对应的行？我这样问是因为很多答案都假设相反。您使用的是什么数据库服务器？为了澄清，您是说表2中有一些行在表1中没有对应的行？我这样问是因为很多答案都是相反的，只是在前面加上“INSERT-INTO[table 3]”，然后在前面加上“INSERT-INTO[table 3]”