在工作中偶尔需要将多行数据转换成一行显示，由于不经常使用，故此处记录一下方便下次查看
listagg(expr1,expr2) within group(order by expr3)
expr1：需要进行转换的列，可以单列也可以是多列
expr2：列与列之间的分隔符，比如逗号（，）、分号（；）等等
expr3：排序列
接下来官网的示例说明
需求一：汇总列出了hr.employees表中部门ID=30中的所有员工，并按雇用日期和姓名排序：
SELECT LISTAGG(last_name, '; ')
WITHIN GROUP (ORDER BY hire_date, last_name) "所有员工",
MIN(hire_date) "最小雇佣日期"
FROM employees
WHERE department_id = 30;
所有员工 最小雇佣日期
------------------------------------------------------------ ---------
Raphaely; Khoo; Tobias; Baida; Himuro; Colmenares 2020-02-25
需求二：以组集合汇总示例针对hr.employees表中的每个部门ID ，按其雇用日期的顺序列出了该部门中的员工：
SELECT department_id "部门.",
LISTAGG(last_name, '; ') WITHIN GROUP (ORDER BY hire_date) "部门下的所有员工"
FROM employees
GROUP BY department_id
ORDER BY department_id;
部门. 部门下的所有员工
------ ------------------------------------------------------------
10 Whalen
20 Hartstein; Fay
30 Raphaely; Khoo; Tobias; Baida; Himuro; Colmenares
40 Mavris
50 Kaufling; Ladwig; Rajs; Sarchand; Bell; Mallin; Weiss; Davie
s; Marlow; Bull; Everett; Fripp; Chung; Nayer; Dilly; Bissot
; Vollman; Stiles; Atkinson; Taylor; Seo; Fleaur; Matos; Pat
el; Walsh; Feeney; Dellinger; McCain; Vargas; Gates; Rogers;
Mikkilineni; Landry; Cabrio; Jones; Olson; OConnell; Sulliv
an; Mourgos; Gee; Perkins; Grant; Geoni; Philtanker; Markle
60 Austin; Hunold; Pataballa; Lorentz; Ernst
70 Baer
. . .
需求三：以下示例与上一示例相同，不同之处在于它包含该ON OVERFLOW TRUNCATE子句。出于本示例的目的，假定返回值的最大长度是人为的200字节的小数字。由于部门50的员工列表超过200个字节，因此该列表被截断并附加了最终定界符’ ;’，指定的截断指示符’ …‘和截断值的数量’ (23)’。
SELECT department_id "部门.",
LISTAGG(last_name, '; ' ON OVERFLOW TRUNCATE '...')
WITHIN GROUP (ORDER BY hire_date) "部门下的所有员工"
FROM employees
GROUP BY department_id
ORDER BY department_id;
部门. 部门下的所有员工
------ ------------------------------------------------------------
10 Whalen
20 Hartstein; Fay
30 Raphaely; Khoo; Tobias; Baida; Himuro; Colmenares
40 Mavris
50 Kaufling; Ladwig; Rajs; Sarchand; Bell; Mallin; Weiss; Davie
s; Marlow; Bull; Everett; Fripp; Chung; Nayer; Dilly; Bissot
; Vollman; Stiles; Atkinson; Taylor; Seo; Fleaur; ... (23)
70 Baer
. . .
需求四：分析示例，对于2003年9月1日之前雇用的每个员工，该员工的部门，雇用日期以及该部门中的所有其他员工也在2003年9月1日之前雇用
SELECT department_id "部门", hire_date "雇佣日期", last_name "员工",
LISTAGG(last_name, '; ') WITHIN GROUP (ORDER BY hire_date, last_name)
OVER (PARTITION BY department_id) as "其他员工"
FROM employees
WHERE hire_date < '01-SEP-2003'
ORDER BY "Dept", "Date", "Name";
部门 雇佣日期 员工 其他员工
----- --------- --------------- ---------------------------------------------
30 07-DEC-02 Raphaely Raphaely; Khoo
30 18-MAY-03 Khoo Raphaely; Khoo
40 07-JUN-02 Mavris Mavris
50 01-MAY-03 Kaufling Kaufling; Ladwig
50 14-JUL-03 Ladwig Kaufling; Ladwig
70 07-JUN-02 Baer Baer
90 13-JAN-01 De Haan De Haan; King
90 17-JUN-03 King De Haan; King
100 16-AUG-02 Faviet Faviet; Greenberg
100 17-AUG-02 Greenberg Faviet; Greenberg
110 07-JUN-02 Gietz Gietz; Higgins
110 07-JUN-02 Higgins Gietz; Higgins