在SQL中,collect_set
函數(shù)用于收集給定列中不重復(fù)的值,并將這些值存儲為一個(gè)集合。通常用于對數(shù)據(jù)進(jìn)行去重操作。
語法如下:
collect_set(column_name)
示例:
假設(shè)有一個(gè)表employee
,包含department_id
和employee_name
兩列數(shù)據(jù),現(xiàn)在想要查找每個(gè)部門中的唯一員工姓名,可以使用collect_set
函數(shù)進(jìn)行操作:
SELECT department_id, collect_set(employee_name) as unique_employees
FROM employee
GROUP BY department_id;
在上面的示例中,collect_set(employee_name)
將返回每個(gè)部門中唯一的員工姓名集合。