GREATEST和LEAST

SELECT GREATEST(25, 6, 7, 10, 20, 54);  --  returns 54
SELECT LEAST(25, 6, 7, 10, 20, 54);  --  returns 6

SELECT GREATEST('D','A', 'B', 'C','d','e','E'); -- returns 'E'
SELECT LEAST('D','A', 'B', 'C','d','e','E','a'); -- returns 'a'

SELECT GREATEST(6, NULL); -- result: 6
SELECT LEAST(6, NULL); -- result: 6

GREATEST和MAX的区别

MAX为 聚合函数，在一个数据表的某一字段列中，取出最大值数据

PostgreSQL GREATEST & LEAST https://www.yetaozi.cn/postgresql/greatest-least-function