在INSERT中对CASE WHEN的SQL语句感到困惑

Question

我有以下SQL语句（适用于SQL Server）：

INSERT INTO t1 (c1, c2) 
VALUES (1, CASE WHEN (SELECT MAX(c2) FROM t1 AS maxV) IS NOT NULL THEN maxV+1 ELSE 1 END);

我收到错误：“无效的列名'maxV'”

为什么？

Answer 1

尝试使用COALESCE：

INSERT INTO t1 (c1, c2) 
SELECT 1, COALESCE(MAX(c2), 0) + 1
FROM t1

Answer 2

试试这个......

INSERT INTO t1 (c1, c2) 
VALUES (
    1, 
    CASE 
        WHEN (SELECT MAX(c2) FROM t1) IS NOT NULL 
        THEN (SELECT MAX(c2)+1 FROM t1)
        ELSE 1 
    END);

Answer 3

另一种方式......

INSERT INTO t1 (c1, c2) 
VALUES (1, ISNULL(SELECT MAX(c2) FROM t1, 0)+1);