我怎么能这样做ORACLE查询？

Question

我有2个表：表1 和表2 ：

表1 有2列

表2 有3列

ID 列 Table1 和 Table2

表1 的 ID 比表2

更多

但我希望有一个查询能够将 Table1 的所有 ID 返回给 Table2

的第3列>

表1

+------+-------+
| Id   | Col2  |
+------+-------+
|    1 | 20000 |
|    2 | 20001 |
|    3 | 20002 |
|    4 | 20003 |
+------+-------+

表2

+------+------+------+
| Col1 | Id   | Col3 |
+------+------+------+
|  100 |    1 |   25 |
|  100 |    2 |   50 |
|  100 |    4 |   40 |
+------+------+------+

我希望有这张表：

表3

+------+-------+--------+
| Col1 | Col2  |  Col3  |
+------+-------+------+-+
|    1 | 20000 |     25 |
|    2 | 20001 |     50 |
|    3 | 20002 |      0 |
|    4 | 20003 |     40 |
+------+-------+------+-+

Answer 1

如果你想要这个“但我希望有一个查询，它返回Table1的所有Id和Table2的第3列”：

select t1.id, t2.Col3 from table1 t1 left join table2 t2 on t1.id = t2.id

如果你想得到表3：

select t1.id as Col1, t1.Col2, COALESCE(t2.Col1, 100) as Col3, COALESCE(t2.Col3, 0) as Col4 
from table1 t1 left join table2 t2 on t1.id = t2.id

Answer 2

SQL Fiddle

Oracle 11g R2架构设置：

CREATE TABLE Table1 ( Id, Col2 ) AS
          SELECT 1, 20000 FROM DUAL
UNION ALL SELECT 2, 20001 FROM DUAL
UNION ALL SELECT 3, 20002 FROM DUAL
UNION ALL SELECT 4, 20003 FROM DUAL;

CREATE TABLE Table2 ( Col1, Id, Col3 ) AS
          SELECT 100, 1, 25 FROM DUAL
UNION ALL SELECT 100, 2, 50 FROM DUAL
UNION ALL SELECT 100, 4, 40 FROM DUAL;

查询1 ：

SELECT t1.Id,
       Col2,
       COALESCE( Col1, 100 ) AS Col1,
       COALESCE( Col3, 0 ) AS Col3
FROM   Table1 t1
       LEFT OUTER JOIN
       Table2 t2
       ON ( t1.Id = t2.Id )

<强> Results ：

| ID |  COL2 | COL1 | COL3 |
|----|-------|------|------|
|  1 | 20000 |  100 |   25 |
|  2 | 20001 |  100 |   50 |
|  4 | 20003 |  100 |   40 |
|  3 | 20002 |  100 |    0 |