条件分支

通过年龄判断是否成年。

SELECT CASE WHEN 25 > 18 THEN '成年' ELSE '未成年' END AS [判断];

判断
成年

SELECT IIF(25 > 18, '成年', '未成年') AS [判断1];

判断1
成年

返回首个非空值。

SELECT COALESCE(NULL, 1, 2) AS [结果];

结果
1

SELECT COALESCE(3, NULL, 4) AS [结果1];

结果1
3

SELECT COALESCE(5, 6, NULL) AS [结果2];

结果2
5

SELECT COALESCE(NULL, 1) AS [结果];

结果
1

SELECT COALESCE(2, NULL) AS [结果1];

结果1
2

SELECT IFNULL(NULL, 1) AS [结果];

结果
1

SELECT IFNULL(2, NULL) AS [结果1];

结果1
2

NULLIF(x, y) 用法，两个参数相同返回 NULL ，不相同则返回第一个参数。

SELECT NULLIF('A', 'B') AS [结果];

结果
A