在 WHERE 子句中为 IN 条件声明变量

Posted 2023-03-23

【中文标题】在 WHERE 子句中为 IN 条件声明变量

【英文标题】：Declare variable for IN condition in WHERE clause

【发布时间】：2020-02-06 08:05:42

【问题描述】：

我有下表，你也可以在SQL Fiddlehere找到：

CREATE TABLE Flows (
    Flow_Date DATE,
    Product TEXT,
    FlowType TEXT,
    Country TEXT,
    Quantity VARCHAR(255)
);

INSERT INTO Flows
(Flow_Date, Product, FlowType, Country, Quantity)
VALUES 
("2019-05-23", "Product A", "Inbound", "DE", "400"),
("2019-05-23", "Product A", "Inbound", "DE", "400"),
("2019-05-23", "Product B", "Inbound", "NL", "500"),
("2019-05-23", "Product B", "Inbound", "NL", "500"),
("2019-05-23", "Product A", "Outbound", "FR", "300"),
("2019-05-23", "Product A", "Outbound", "FR", "300"),
("2019-05-23", "Product B", "Outbound", "US", "200"),
("2019-05-23", "Product B", "Outbound", "US", "200"),
("2019-05-24", "Product A", "Inbound", "DE", "900"),
("2019-05-24", "Product A", "Inbound", "DE", "900"),
("2019-05-24", "Product B", "Inbound", "NL", "800"),
("2019-05-24", "Product B", "Inbound", "NL", "800"),
("2019-05-24", "Product A", "Outbound", "FR", "650"),
("2019-05-24", "Product A", "Outbound", "FR", "650"),
("2019-05-24", "Product B", "Outbound", "US", "450"),
("2019-05-24", "Product B", "Outbound", "US", "450"),
("2019-05-25", "Product A", "Inbound", "DE", "900"),
("2019-05-25", "Product A", "Inbound", "DE", "900"),
("2019-05-25", "Product B", "Inbound", "NL", "800"),
("2019-05-25", "Product B", "Inbound", "NL", "800"),
("2019-05-25", "Product A", "Outbound", "FR", "650"),
("2019-05-25", "Product A", "Outbound", "FR", "650"),
("2019-05-25", "Product B", "Outbound", "US", "450"),
("2019-05-25", "Product B", "Outbound", "US", "450"),
("2019-05-26", "Product A", "Inbound", "DE", "900"),
("2019-05-26", "Product A", "Inbound", "DE", "900"),
("2019-05-26", "Product B", "Inbound", "NL", "800"),
("2019-05-26", "Product B", "Inbound", "NL", "800"),
("2019-05-26", "Product A", "Outbound", "FR", "650"),
("2019-05-26", "Product A", "Outbound", "FR", "650"),
("2019-05-26", "Product B", "Outbound", "US", "450"),
("2019-05-26", "Product B", "Outbound", "US", "450");

我使用以下查询从该表中获取数据：

SELECT Flow_Date, Product, FlowType, Country
FROM Flows
WHERE Flow_Date BETWEEN ("2019-05-23 00:00:00") AND ("2019-05-25 23:59:59")
AND Country IN ("DE","NL")
GROUP BY 1,2,3,4;

到目前为止，这一切都完美无缺。

---

但是，现在我想在语句的WHERE 子句中为IN 条件设置一个变量。 因此，我尝试使用以下方法：

SET @country = ("DE", "NL");
SELECT Flow_Date, Product, FlowType, Country
FROM Flows
WHERE Flow_Date BETWEEN ("2019-05-23 00:00:00") AND ("2019-05-25 23:59:59")
AND Country IN @country
GROUP BY 1,2,3,4;

但是，我收到错误Operand should contain 1 column(s)。

我需要对我的代码进行哪些更改才能使其正常工作？

【问题讨论】：

在这里查看解决方案：***.com/questions/4723100/…

我收到错误Operand should contain 1 column(s) 这是SET @country = ("DE", "NL"); 语句的错误。

我使用以下查询从该表中获取数据： GROUP BY by all output fieldlist？完全删除 GROUP BY 子句，但添加 DISTINCT。或者添加一些聚合操作，例如，SUM(Quantity)...

【参考方案1】：

SET @country = "DE,NL";

SELECT DISTINCT Flow_Date, Product, FlowType, Country
FROM Flows
WHERE Flow_Date BETWEEN ("2019-05-23 00:00:00") AND ("2019-05-25 00:00:00")
  AND FIND_IN_SET(Country, @country);

fiddle

【讨论】：

谢谢。正是我需要的。 sqlfiddle.com/#!9/e83241/39

@Michi 按所有输出字段分组会导致过度排序。请参阅我对此问题的评论。