Question

假设我有这样的表：

id: PRIMARY INT
price: INT (in dollars)
typeOfHouse: TINYINT (enumerated house types)

并且存在元组，假设（id = 3，price = 1243，typeOfHouse = 20）。

现在我想选择2个便宜的房子和2个费用较低的房子（2个，2个）。这可以通过两个查询（UNION）完成：

SELECT * FROM houses WHERE typeOfHouse=20 AND price>=1243 ORDER BY price LIMIT 3
SELECT * FROM houses WHERE typeOfHouse=20 AND price<=1243 ORDER BY price DESC LIMIT 3

这是一个假设的例子，条件通常要复杂得多，所以问题是 - 可以在一个查询中更快地完成这项工作，所以条件选择不会不得不进行两次。

Answer 1

你有什么好。您可以在一个查询中与UNION合并：

    SELECT * 
    FROM houses 
    WHERE typeOfHouse = 20       --- there may be more more houses
      AND price = 1243           --- with same price
UNION ALL
    SELECT * 
    FROM houses 
    WHERE typeOfHouse = 20 
      AND price > 1243 
    ORDER BY price 
    LIMIT 2
UNION ALL
    SELECT * 
    FROM houses 
    WHERE typeOfHouse = 20 
      AND price < 1243 
    ORDER BY price DESC 
    LIMIT 2

如果price上有索引，或者甚至更好 - (typeOfHouse, price)上的复合索引，则无需担心性能。

Answer 2

您可以使用BETWEEN运算符，例如

SELECT * FROM houses WHERE typeOfHouse=20 AND price BETWEEN 1241 AND 1245 ORDER BY price

Mysql查询结果围绕一些ID

2 个答案: