常用listagg聚合函数

LISTAGG(column, [separator]) WITHIN GROUP (ORDER BY order_by_clause)

column：你想要连接起来的列。
[separator]：可选参数，用于指定列值之间的分隔符。如果不指定，则默认没有分隔符。
WITHIN GROUP (ORDER BY order_by_clause)：指定连接时列值的排序方式。这是必须的，因为 LISTAGG 需要知道如何对值进行排序以生成最终的字符串。

用法

SELECT department_id,  LISTAGG(employee_name, ', ') WITHIN GROUP (ORDER BY employee_name) ||',' AS employees  
FROM employees  
GROUP BY department_id;

LISTAGG(employee_name, ‘, ‘) ：这里表示拼接wy字段，使用’，‘隔开，
||’,’ ： 结尾这个表示字段最后也加上‘,’逗号
group (order by l_ztbh)按照 l_ztbh字段进行排序

也可用 XMLAGG代替上述操作

SELECT department_id,  XMLELEMENT(NAME "employees",  XMLAGG(XMLELEMENT(NAME "employee", employee_name)  ORDER BY employee_name)).EXTRACT('//text()') AS employees_xml  
FROM employees  
GROUP BY department_id;```