哪里有 SQL 子查询

Question

我有以下查询：

SELECT 
`id`, `firstName`, `lastName`, `nickName`, `email`, 
`verificationCode`, `roleId`, `profileImageId`, `statusId`, `createdAt`, 
(SELECT COUNT(*) FROM RecipeStores WHERE RecipeStores.userId = User.id) AS `countStoredRecipes`, 
(SELECT COUNT(*) FROM RecipeFavorites WHERE RecipeFavorites.userId = User.id) AS `countLikedRecipes`, 
(SELECT COUNT(*) FROM Recipes WHERE Recipes.createdById = User.id) AS `countCreatedRecipes` 
FROM `Users` AS `User` WHERE `User`.`countStoredRecipes` >= 2;

然而，它不起作用。我想通过子查询的结果进行过滤。

我知道子查询不能再作为一个列来工作，所以我希望有其他方法可以做到这一点。

Answer 1

MySQL 实现了标准 SQL 的扩展，允许您在 HAVING 子句中引用别名：

SELECT 
    `id`, `firstName`, `lastName`, `nickName`, `email`, 
    `verificationCode`, `roleId`, `profileImageId`, `statusId`, `createdAt`, 
    (SELECT COUNT(*) FROM RecipeStores rs WHERE rs.userId = u.id) AS `countStoredRecipes`, 
    (SELECT COUNT(*) FROM RecipeFavorites rf WHERE rf.userId = u.id) AS `countLikedRecipes`, 
    (SELECT COUNT(*) FROM Recipes r WHERE r.createdById = u.id) AS `countCreatedRecipes` 
FROM `Users` u
HAVING `User`.`countStoredRecipes` >= 2;

我不是这种技术的忠实粉丝：这确实是定制的 MySQL 语法，在任何其他数据库中都不会运行。

一个更标准的选项是将现有查询转换为子查询，并在外部范围内进行过滤：

SELECT *
FROM (
    SELECT 
        `id`, `firstName`, `lastName`, `nickName`, `email`, 
        `verificationCode`, `roleId`, `profileImageId`, `statusId`, `createdAt`, 
        (SELECT COUNT(*) FROM RecipeStores rs WHERE rs.userId = u.id) AS `countStoredRecipes`, 
        (SELECT COUNT(*) FROM RecipeFavorites rf WHERE rf.userId = u.id) AS `countLikedRecipes`, 
        (SELECT COUNT(*) FROM Recipes r WHERE r.createdById = u.id) AS `countCreatedRecipes` 
    FROM `Users` u
) t
WHERE `countStoredRecipes` >= 2;

在 MySQL 的最新版本中，您可以使用横向连接：

SELECT 
    `id`, `firstName`, `lastName`, `nickName`, `email`, 
    `verificationCode`, `roleId`, `profileImageId`, `statusId`, `createdAt`, 
    rs.*, rf.*, r.* 
    () AS  
FROM `Users` u
INNER JOIN LATERAL (
    SELECT COUNT(*) AS `countStoredRecipes` 
    FROM RecipeStores rs 
    WHERE rs.userId = u.id
) rs ON rs.`countStoredRecipes`>= 2
LEFT JOIN LATERAL (
    SELECT COUNT(*) AS `countLikedRecipes` 
    FROM RecipeFavorites rf 
    WHERE rf.userId = u.id
) rf ON true
LEFT JOIN LATERAL (
    SELECT COUNT(*) AS `countCreatedRecipes` 
    FROM Recipes r 
    WHERE r.createdById = u.id
) r ON true

哪里有 SQL 子查询

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