LISTAGG

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1. 说明

对数据集排序后，再串行计算

1.1 如果是作为单行输出计算函数，会操作所有的行，然后只返回一行。

SELECT LISTAGG(last_name, '; ')
WITHIN GROUP (ORDER BY hire_date, last_name) "Emp_list",
MIN(hire_date) "Earliest"
FROM employees
WHERE department_id = 30;
Emp_list Earliest
------------------------------------------------------------ ---------
Raphaely; Khoo; Tobias; Baida; Himuro; Colmenares 07-DEC-02

1.2 如果是操作由group by 传来的组集合，LISTAGG会把每一组作为一个计算单位，为每一组返回一行。

SELECT department_id "Dept.",

LISTAGG(last_name, '; ') WITHIN GROUP (ORDER BY hire_date) "Employees"
FROM employees
GROUP BY department_id
ORDER BY department_id;
Dept. Employees
------ ------------------------------------------------------------
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

1.3 如果后面后面有分析函数时，LISTAGG会计算分区集合。

SELECT department_id "Dept", hire_date "Date", last_name "Name",
LISTAGG(last_name, '; ') WITHIN GROUP (ORDER BY hire_date, last_name)
OVER (PARTITION BY department_id) as "Emp_list"
FROM employees
WHERE hire_date < '01-SEP-2003'
ORDER BY "Dept", "Date", "Name";
Dept Date Name Emp_list
----- --------- --------------- ---------------------------------------------
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

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