OceanBase LISTAGG

2021-06-24 16:21 更新

LISTAGG 函數(shù)用于列轉(zhuǎn)行，LISTAGG 對(duì) ORDER BY 子句中指定的每個(gè)組內(nèi)的數(shù)據(jù)進(jìn)行排序，然后合并度量列的值。作為單個(gè)集合的聚合函數(shù)，LISTAGG 對(duì)所有行進(jìn)行操作并返回單個(gè)輸出行。作為組集聚合，LISTAGG 將對(duì) GROUP BY 子句定義的每個(gè)組進(jìn)行操作并返回輸出行。作為分析函數(shù)，LISTAGG 基于 query_partition_clause 中的一個(gè)或多個(gè)表達(dá)式將查詢結(jié)果集分為幾組。

語(yǔ)法

LISTAGG（measure_expr [,'delimiter']）WITHIN GROUP (order_by_clause)
[OVER query_partition_clause]

作為分析函數(shù)使用時(shí)，您需要使用窗口函數(shù)的完整語(yǔ)法，它對(duì)一組行的集合進(jìn)行計(jì)算并返回多個(gè)值。作為聚合函數(shù)使用時(shí)，該函數(shù)對(duì)一組行的集合進(jìn)行聚合計(jì)算，結(jié)果只能返回一個(gè)值，此時(shí)不需要加 OVER 關(guān)鍵字。

參數(shù)

參數(shù)

說(shuō)明

OVER

使用 OVER 子句定義窗口進(jìn)行計(jì)算。

measure_expr

可以是任何表達(dá)式。度量列中的空值將被忽略。

delimiter

指定用于分隔度量值的字符串。此子句是可選的，默認(rèn)為 NULL。

返回類型

如果度量列是 RAW 的，則返回?cái)?shù)據(jù)類型為 RAW，否則返回值為 VARCHAR2 型。

示例

分析函數(shù)示例

建表 employees，并向里面插入數(shù)據(jù)，執(zhí)行以下語(yǔ)句：

CREATE TABLE employees (department_id INT,manager_id INT,last_name varchar(50),hiredate varchar(50),SALARY INT);
INSERT INTO employees VALUES(30, 100, 'Raphaely', '2017-07-01', 1700);
INSERT INTO employees VALUES(30, 100, 'De Haan', '2018-05-01',11000);      
INSERT INTO employees VALUES(40, 100, 'Errazuriz', '2017-07-21', 1400);
INSERT INTO employees VALUES(50, 100, 'Hartstein', '2019-05-01',14000);     
INSERT INTO employees VALUES(50, 100, 'Raphaely', '2017-07-22', 1700);
INSERT INTO employees VALUES(70, 100, 'Weiss',  '2019-07-11',13500);     
INSERT INTO employees VALUES(90, 100, 'Russell', '2019-10-05', 13000);
INSERT INTO employees VALUES(90,100, 'Partners',  '2018-12-01',14000);

查詢 2019 年 10 月 10 日之前雇用的雇員，以及該雇員的部門，雇用日期以及該部門中的其他雇員。執(zhí)行以下語(yǔ)句：

SELECT department_id "Dept", hiredate "Date", last_name "Name",LISTAGG(last_name, '; ') WITHIN GROUP 
(ORDER BY hiredate, last_name) OVER (PARTITION BY department_id) as "Emp_list"
FROM employees WHERE hiredate < '2019-10-10' ORDER BY "Dept", "Date", "Name";

查詢結(jié)果如下：

+------+------------+-----------+---------------------+
| Dept | Date       | Name      | Emp_list            |
+------+------------+-----------+---------------------+
|   30 | 2017-07-01 | Raphaely  | Raphaely; De Haan   |
|   30 | 2018-05-01 | De Haan   | Raphaely; De Haan   |
|   40 | 2017-07-21 | Errazuriz | Errazuriz           |
|   50 | 2017-07-22 | Raphaely  | Raphaely; Hartstein |
|   50 | 2019-05-01 | Hartstein | Raphaely; Hartstein |
|   70 | 2019-07-11 | Weiss     | Weiss               |
|   90 | 2018-12-01 | Partners  | Partners; Russell   |
|   90 | 2019-10-05 | Russell   | Partners; Russell   |
+------+------------+-----------+---------------------+

聚合函數(shù)示例

建表 employees，并向里面插入數(shù)據(jù)，執(zhí)行以下語(yǔ)句：

CREATE TABLE employees (department_id INT,manager_id INT,last_name varchar(50),hiredate varchar(50),SALARY INT);
INSERT INTO employees VALUES(30, 100, 'Raphaely', '2017-07-01', 1700);
INSERT INTO employees VALUES(30, 100, 'De Haan', '2018-05-01',11000);      
INSERT INTO employees VALUES(30, 100, 'Errazuriz', '2017-07-01', 1400);
INSERT INTO employees VALUES(30, 100, 'Hartstein', '2019-05-01',14000);     
INSERT INTO employees VALUES(30, 100, 'Raphaely', '2017-07-01', 1700);
INSERT INTO employees VALUES(30, 100, 'Weiss',  '2019-07-01',13500);     
INSERT INTO employees VALUES(30, 100, 'Russell', '2019-07-01', 13000);
INSERT INTO employees VALUES(30,100, 'Partners',  '2018-12-01',14000);

查詢第 30 部門的所有員工，并按雇用日期和姓氏排序。執(zhí)行以下語(yǔ)句：

SELECT LISTAGG(last_name, '; ') WITHIN GROUP (ORDER BY hiredate, last_name)  as "Emp_list", 
MIN(hiredate) as "Earliest" FROM employees WHERE department_id = 30;

查詢結(jié)果如下：

+-----------------------------------------------------------------------------+------------+
| Emp_list                                                                    | Earliest   |
+-----------------------------------------------------------------------------+------------+
| Errazuriz; Raphaely; Raphaely; De Haan; Partners; Hartstein; Russell; Weiss | 2017-07-01 |
+-----------------------------------------------------------------------------+------------+
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