Question

我目前有两张桌子需要加入。

第一张表是一张大表，数百万条记录。第二个是匹配表。我想加入2桌。预期结果的表格如下所示。我需要有关如何编写SQL以加入2个表的提示。

    Table 1

    ID X   Column X
    1      X1
    2      X2
    3      X3
    4      X4
    5      X5
    6      X6
    ...  ...
    the list goes on

    Table 2

    ID   Column Y
    1    Y1
    3    Y2
    6    Y3
    11   Y4


    Intended result

    ID X   Column X  Column Y
    1      X1        Y1
    2      X2        Y1
    3      X3        Y2
    4      X4        Y2
    5      X5        Y2
    6      X6        Y3
    7      X7        Y3
    8      X8        Y3
    9      X9        Y3
    10     X10       Y3
    11     X11       Y4
    12     X12       Y4

Answer 1

SELECT idX, columnX, columnY
FROM (
    SELECT id, columnY, @prevID AS prevID, @prevID := id
    FROM table2
    CROSS JOIN (SELECT @prevID := NULL) init
    ORDER BY id DESC) AS t2
JOIN table1 AS t1 ON t1.idX >= t2.id AND (t2.prevID IS NULL OR t1.idX < t2.prevID)

DEMO

Answer 2

SELECT T1.IDX, T1.ColumnX , T2.ColumnY FROM TABLE1 T1
INNER JOIN TABLE2 T2 ON T1.IDX = T2.ID

Answer 3

我想要获得你需要使用内连接的预期结果：

select t1.id, t1.X, t2.Y from table1 t1 inner join table2 t2 on t1.id = t2.id;

用户链接：

http://blog.sqlauthority.com/2009/04/13/sql-server-introduction-to-joins-basic-of-joins/

http://www.codinghorror.com/blog/2007/10/a-visual-explanation-of-sql-joins.html

Full Outer Join in MySQL

编辑：

哦，我没有检查行不匹配。我试过这种方式。它对我有用：

select t1.id, t1.x,
if(t2.y != 'null',t2.y,(select y from table2 t3 where t3.id < t1.id order by t3.id desc limit 1)) as 'y'
from table1 t1 left join table2 t2 on t1.id = t2.id;

连接表与范围ID匹配

3 个答案: