MySQL WHERE 子句中未引用 CTE

Question

我无法理解为什么 CTE 不能从 WHERE 子句中引用。在下面的代码中，第一个查询工作正常，但在第二个查询中，只需将 WHERE 子句中的值替换为计算该值的 CTE，就会产生错误“Unknown column 'cte' in 'where clause'".

# 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", "1301",   '2019-10-30',   76.6),
("T", "1301",   '2019-10-31',   77.6),
("T", "1301",   '2019-11-01',   77.2),
("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),
("T", "1333",   '2019-10-29',   13.9),
("T", "1333",   '2019-10-30',   13.8),
("T", "1333",   '2019-10-31',   14.3),
("T", "1333",   '2019-11-01',   14.4);

Answer 1

你可以这样做：

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 ...
cte 需要命名列；这就是为什么我添加 as code.

参见 DB Fiddle 中的运行示例。

Answer 2

听起来您正在将 cte 视为某种变量，而不是将其视为虚拟 table。

你做不到IN (cte)就像你做不到IN (sometablename)一样；它需要 IN (select somecol from sometablename).

Answer 3

您可以使用 TABLE 关键字通过名称引用 cte 或另一个 table（不使用它的子选择）。

WITH
    cte AS (SELECT '1332')    
SELECT * FROM stock_prices
WHERE Country_Exchange_Code = 'T' AND Stock_Code IN (TABLE cte);

fiddle

MySQL WHERE 子句中未引用 CTE

MySQL CTE not referenced in WHERE clause

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