针对特定 table 优化查询

Question

我有一个 table，我正在寻找提高其性能的方法。下面是要执行的查询列表。

dbo.CustomersSmallOrders
(
    ID INT NOT NULL IDENTITY(1,1) PRIMARY KEY CLUSTERED,
    CustomerName VARCHAR(MAX) NOT NULL,
    OrderDate DATETIME NOT NULL,
    Quantity INT NOT NULL,
    Amount DECIMAL(15,2) NOT NULL,
    AvailableAmount DECIMAL(15,2) NOT NULL,
    Type TINYINT NOT NULL,
    Status TINYINT NOT NULL
)

能否请您帮我重写以下查询并向 table 添加索引以提高其性能？

SELECT *
FROM CustomersSmallOrders
WHERE Left(CustomerName, 4) = 'Levis'

SELECT *
FROM CustomersSmallOrders
WHERE DateDiff(month, OrderDate, GetDate()) >= 30

SELECT *
FROM CustomersSmallOrders
WHERE Quantity * 2 < 3400

SELECT 
    SUM(CASE 
            WHEN Type = 2 AND STATUS IN (0, 1, 2) THEN Amount 
            ELSE 0 
        END)
    ,SUM(CASE 
             WHEN Type = 1 AND STATUS IN (0, 1) THEN Amount 
             ELSE 0 
         END)
    ,SUM(CASE 
             WHEN Type = 2 AND STATUS IN (0, 1) THEN Amount - AvailableAmount 
             ELSE 0 
         END)
FROM CustomersSmallOrders
WHERE STATUS IN (0, 1, 2)

Answer 1

查询改进：

正如 Martin Smith 所说，第一个查询可以转换为

SELECT TOP 0 * FROM CustomersSmallOrders

因为矛盾

如果是

WHERE Left(CustomerName, 5) = 'Levis'

然后将条件更改为

WHERE CustomerName LIKE 'Levis%'

将保留查询 sargable 并允许使用索引。

可以通过更改条件并在 OrderDate 上添加索引来改进第二个查询：

SELECT *
FROM CustomersSmallOrders
WHERE OrderDate <= DATEADD(Mounth, -30, GetDate())

第三个（添加数量索引）：

SELECT *
FROM CustomersSmallOrders
WHERE Quantity < 1700

第 4 - 在 STATUS 上添加一个索引，其中还包含 Type、Amount 和 AvailableAmount（虽然我不明白他为什么想要两次 Amount。我认为这可能是一个错误，他只想要 1 列输出） :

SELECT 
SUM(CASE 
        WHEN Type = 2 THEN Amount 
        ELSE 0 
    END)
,SUM(CASE 
         WHEN Type = 1 AND STATUS IN (0, 1) THEN Amount 
         ELSE 0 
     END)
,SUM(CASE 
         WHEN Type = 2 AND STATUS IN (0, 1) THEN Amount - AvailableAmount 
         ELSE 0 
     END)
FROM CustomersSmallOrders
WHERE STATUS IN (0, 1, 2)

针对特定 table 优化查询

Optimizing queries for the particular table

sql-server

indexing

query-optimization

query-performance

query-tuning