如何缩短 T-SQL 中的 WHERE 子句

Posted 2023-02-26

【中文标题】如何缩短 T-SQL 中的 WHERE 子句

【英文标题】：How to shorten WHERE clause in T-SQL

【发布时间】：2021-12-27 13:53:14

【问题描述】：

我正在 SQL Server 2019 中为我的数据库编写以下视图，它工作正常。我觉得我的WHERE 子句太长了，也许你写的更短的子句会满足我的需要。 WHERE 子句也可以很好地过滤视图。这似乎太新手了，因此任何高级解决方案都值得赞赏。

CREATE VIEW dbo.View1 
AS 
    SELECT
        Table1.QNO,
        Table1.QRevNO,
        Table1.QID,
        Table1.LStatus AS Status,
        Table1.StatusCode AS [Status Code],
        CASE
            WHEN Table1.IsProject = 1 THEN 'Goods'
            WHEN Table1.IsProject = 2 THEN 'Services'
            ELSE 'Project'
        END AS [Product Type],
        Table2.ProductGroup AS [Group],
        Table2.TotalOfItem AS [Sales],
        Table3.CompanyName AS [Customer]
    FROM 
        dbo.Table1
    INNER JOIN 
        dbo.Table2 ON Table1.QID = Table2.QID
    INNER JOIN 
        dbo.Table3 ON Table3.CompanyID = Table1.CompanyID
    WHERE 
        Table1.RevActivated = 1
        AND ((DATEPART(YEAR, Table1.ORDate) = DATEPART(YEAR, GETDATE())
             OR (DATEPART(YEAR, Table1.PIDate) = DATEPART(YEAR, GETDATE())
        AND Table1.ORDate IS NULL)
             OR (DATEPART(YEAR, Table1.PODate) = DATEPART(YEAR, GETDATE())
        AND Table1.ORDate IS NULL
        AND Table1.PIDate IS NULL)
    OR (DATEPART(YEAR, Table1.BADate) = DATEPART(YEAR, GETDATE())
      AND Table1.ORDate IS NULL
      AND Table1.PIDate IS NULL
      AND Table1.PODate IS NULL)
    OR (DATEPART(YEAR, Table1.OCDate) = DATEPART(YEAR, GETDATE())
      AND Table1.ORDate IS NULL
      AND Table1.PIDate IS NULL
      AND Table1.PODate IS NULL
      AND Table1.BADate IS NULL)
    OR (DATEPART(YEAR, Table1.ShipDate) = DATEPART(YEAR, GETDATE())
      AND Table1.ORDate IS NULL
      AND Table1.PIDate IS NULL
      AND Table1.PODate IS NULL
      AND Table1.BADate IS NULL
      AND Table1.OCDate IS NULL)
    OR (DATEPART(YEAR, Table1.INVDate) = DATEPART(YEAR, GETDATE())
      AND Table1.ORDate IS NULL
      AND Table1.PIDate IS NULL
      AND Table1.PODate IS NULL
      AND Table1.BADate IS NULL
      AND Table1.OCDate IS NULL
      AND Table1.ShipDate IS NULL)
    OR (DATEPART(YEAR, Table1.PDDate) = DATEPART(YEAR, GETDATE())
      AND Table1.ORDate IS NULL
      AND Table1.PIDate IS NULL
      AND Table1.PODate IS NULL
      AND Table1.BADate IS NULL
      AND Table1.OCDate IS NULL
      AND Table1.ShipDate IS NULL
      AND Table1.INVDate IS NULL)))
GO

【问题讨论】：

似乎你有一个非规范化问题：你不应该有七个相似的日期列，而是你想要一个单独的事件表（外键为Table1），然后你可以做一个简单加入或exists

仅供参考，在WHERE 的列上使用DATEPART 之类的内容会导致您的查询不可搜索，从而导致性能下降。不是检查年份，而是检查日期是否在包含全年的日期范围内。例如>= '2021-01-01' 和< '2022-01'01'。

【参考方案1】：

在 SQL 中，更紧凑的代码不一定是更好的代码。虽然以下内容可能更容易阅读：

...
WHERE t1.RevActivated = 1
  and coalesce(
    t1.ORDate,
    t1.PIDate,
    t1.PODate,
    t1.BADate,
    t1.OCDate,
    t1.ShipDate,
    t1.INVDate,
    t1.PDDate
  ) >= datefromparts(year(getdate()), 1, 1)
  and coalesce(
    t1.ORDate,
    t1.PIDate,
    t1.PODate,
    t1.BADate,
    t1.OCDate,
    t1.ShipDate,
    t1.INVDate,
    t1.PDDate
  ) < datefromparts(year(getdate()) + 1, 1, 1);

其中t1 是alias 的dbo.Table1 表。

即使在您的表格大小超过 Excel 电子表格支持的行数之后，要让这种混乱运行得足够快，这并不容易。您可以尝试使用包含所有 8 个 XyzDate 列的索引，其顺序与您的代码优先考虑它们的顺序完全相同。更好的方法是规范化您的数据模型，而不是使用数据源（当然，除非这不是 DWH）。