Snowflake：IFNULL 不能在 INSERT VALUES 的 subSQL 中使用

Question

尝试在 INSERT VALUES 子句中使用 IFNULL 时出现编译错误。

SQL：

INSERT INTO widgets 
VALUES 
(12, (select ifnull(max(c), 0)+1 from DCSN_Testing where c = 1), 444)

错误：

SQL compilation error: Invalid expression 
[(SELECT (NULLABILITY_EXTERNAL(1)) + 1 AS "IFNULL(MAX(C), 0)+1" 
FROM (VALUES (null)) DCSN_TESTING WHERE TRUE)] in VALUES clause

Answer 1

我通常在 INSERT 的 VALUES 语句中没有子选择，事实上我不记得在我编写的所有 SQL 中做过一个。

也就是说，我建议您尝试以下我称之为“INSERT INTO SELECT”或 Snowflake 文档称之为“使用查询插入单行”的示例，IMO 是编写 SQL 的一种简单/干净的方式.

注意：这已经在 Snowflake 上进行了测试。

-- this is a simple test table, represents your 
--   DCSN_Testing table, results are a value of 5
SELECT IFNULL(MAX(id), 0)+1 FROM first_names;

-- create a test table
DROP TABLE stackoverflow_55387209;
CREATE TABLE stackoverflow_55387209(id NUMBER, 
    new_id NUMBER, other_id  NUMBER);

-- test for your error, results confirm your findings
INSERT INTO stackoverflow_55387209 (id, new_id, other_id)
VALUES (12, (select max(ifnull(id, 0) + 1)  FROM first_names), 444) ;
results:  
SQL compilation error: Invalid expression [(SELECT MAX((NULLABILITY_EXTERNAL(FIRST_NAMES.ID)) + 1) AS "NEW_ID" 
FROM FIRST_NAMES AS FIRST_NAMES)] in VALUES clause

-- rewrite to "INSERT INTO SELECT" type of SQL Query, as described in documentation
--      https://docs.snowflake.net/manuals/sql-reference/sql/insert.html#single-row-insert-using-a-query
INSERT INTO stackoverflow_55387209
SELECT 12, MAX(IFNULL(id, 0) + 1), 444  FROM first_names ;
results:  number of rows inserted = 1