避免插入 SQL 服务器上的唯一冲突

Question

我正在尝试插入一个对 (ProductType, ProductOwnerid) 具有唯一约束的 table，当该键已经存在时，不会触发违反约束的方式。所以我有这个 SQL 按预期工作：

INSERT INTO dbo.Products (ProductType, ProductOwnerId)
SELECT TOP 1 22, 44  FROM dbo.products prods
WHERE NOT EXISTS (
    SELECT prods2.ProductType FROM dbo.products prods2 
    WHERE prods2.ProductType = 22 AND prods2.ProductOwnerId = 44)

这样好吗 SQL 或者我该如何改进它？我不是 TOP 1 的忠实粉丝，我怎样才能使它 readable/better 表现更好？

Answer 1

MERGE 语句是 SQL 处理此类情况的标准方法。

A relational database management system uses SQL MERGE (also called upsert) statements to INSERT new records or UPDATE existing records depending on whether or not a condition matches. It was officially introduced in the SQL:2003 standard, and expanded in the SQL:2008 standard.

它比您的解决方案稍微冗长一点，但我发现它更具可读性。此外，代码的意图非常明确，因为 MERGE 语句专门处理这种情况。

CREATE TABLE products (
    ProductId INT IDENTITY(1, 1), 
    ProductType int, ProductOwnerId INT, 

    CONSTRAINT [unq_type_owner] UNIQUE (ProductType, ProductOwnerId)
);

MERGE INTO dbo.products p
USING (VALUES (22, 44))  AS source(ProductType, ProductOwnerId)
ON p.ProductType = source.ProductType AND p.ProductOwnerId = source.ProductOwnerId

WHEN NOT MATCHED THEN
    INSERT (ProductType, ProductOwnerId)
    VALUES (source.ProductType, source.ProductOwnerId)

-- OPTIONAL OUTPUT
OUTPUT $action, Inserted.* ;

Answer 2

在此查询中，distinct 也可以代替 top 1

INSERT INTO dbo.Products (ProductType, ProductOwnerId)
    SELECT DISTINCT 22, 44  
    FROM dbo.products prods
    WHERE NOT EXISTS (SELECT prods2.ProductType 
                      FROM dbo.products prods2 
                      WHERE prods2.ProductType = 22 AND prods2.ProductOwnerId = 44)

避免插入 SQL 服务器上的唯一冲突

Avoid unique conflicts on insert SQL SERVER

sql

sql-server

performance

database-performance