问题描述
我很难理解为什么无法从CTE
子句中引用WHERE
。
在下面的代码中,第一个查询工作正常,但是在第二个查询中,简单地将WHERE
子句中的值替换为计算该值的CTE,会产生错误“ where子句中的未知列'cte” '”。
# This query works
SELECT * FROM stock_prices
WHERE Country_Exchange_Code = 'T' AND Stock_Code IN ('1332');
# But this query produces an error
WITH
cte AS (SELECT '1332')
SELECT * FROM stock_prices
WHERE Country_Exchange_Code = 'T' AND Stock_Code IN (cte);
# Here is some data to test these two queries with
CREATE TABLE stock_prices (Country_Exchange_Code VARCHAR(2),Stock_Code VARCHAR(4),Date DATE,Close FLOAT);
INSERT INTO stock_prices VALUES
("T","1301",'2019-10-29',75.2),("T",'2019-10-30',76.6),'2019-10-31',77.6),'2019-11-01',77.2),"1332",52.5),49.7),50.8),50.4),"1333",13.9),13.8),14.3),14.4);
解决方法
您可以这样做:
WITH
cte AS (SELECT '1332' as code)
SELECT * FROM stock_prices
WHERE Country_Exchange_Code = 'T' AND Stock_Code IN (select code from cte);
结果:
Country_Exchange_Code Stock_Code Date Close
---------------------- ----------- ----------- -----
T 1332 2019-10-29 52.5
T 1332 2019-10-30 49.7
T 1332 2019-10-31 50.8
T 1332 2019-11-01 50.4
您的查询有两个问题:
-
IN
需要形式为SELECT ...
的形式子查询
- cte需要命名列;这就是为什么我添加
as code
的原因。
请参见DB Fiddle上的运行示例。
,您可以使用cte
关键字通过名称(不使用子选择)来引用TABLE
或其他表。
WITH
cte AS (SELECT '1332')
SELECT * FROM stock_prices
WHERE Country_Exchange_Code = 'T' AND Stock_Code IN (TABLE cte);
,
听起来您正在将cte视为某种变量,而不是将其视为虚拟表。
您不能像做IN (cte)
那样做IN (sometablename)
;它必须为IN (select somecol from sometablename)
。