Question

我有7张相同结构的表格。每个表有2列，其中一列是连接键（但不是主键），第二列是唯一的。

以下是2个表中提到的要求。但是我们需要开发7个表。

TAB1:
=====
CITY    NAME
HYD     RAMU
HYD     KRISH


TAB1:
=====
CITY    NAME
HYD     RAJ
HYD     KRISH

OUTPUT:
=======

CITY   EXIST1   EXIST2
HYD     RAMU     NULL 
HYD     NULL     RAJ
HYD     KRISH    KRISH

Answer 1

4个表的答案 - 将其扩展到7个表格应该相当容易。

Oracle安装程序：

CREATE TABLE t1 ( city, name ) AS
SELECT 'a', 'a' FROM DUAL UNION ALL
SELECT 'a', 'b' FROM DUAL;

CREATE TABLE t2 ( city, name ) AS
SELECT 'a', 'a' FROM DUAL UNION ALL
SELECT 'a', 'c' FROM DUAL;

CREATE TABLE t3 ( city, name ) AS
SELECT 'a', 'b' FROM DUAL UNION ALL
SELECT 'a', 'd' FROM DUAL;

CREATE TABLE t4 ( city, name ) AS
SELECT 'a', 'a' FROM DUAL UNION ALL
SELECT 'a', 'e' FROM DUAL;

<强>查询：

SELECT COALESCE( t1.city, t2.city, t3.city, t4.city ) AS city,
       t1.name AS exist1,
       t2.name AS exist2,
       t3.name AS exist3,
       t4.name AS exist4
FROM   t1
       FULL OUTER JOIN t2
       ON (    t1.city = t2.city
           AND t1.name = t2.name )
       FULL OUTER JOIN t3
       ON (    COALESCE( t1.city, t2.city ) = t3.city
           AND COALESCE( t1.name, t2.name ) = t3.name )
       FULL OUTER JOIN t4
       ON (    COALESCE( t1.city, t2.city, t3.city ) = t4.city
           AND COALESCE( t1.name, t2.name, t3.name ) = t4.name );

<强>输出：

CITY EXIST1 EXIST2 EXIST3 EXIST4
---- ------ ------ ------ ------
a    a      a             a
a    b             b
a           c
a                  d
a                         e

Answer 2

看起来你正在追踪FULL JOIN：

SELECT COALESCE(t1.CITY, t2.CITY), t1.NAME AS EXIST1, t2.NAME AS EXIST2
FROM TAB1 AS t1
FULL JOIN TAB2 ON AS t2 ON t1.CITY = t2.CITY

SQL Query将多个表中的单行转换为表中的单行？

2 个答案: