如何保证索引的使用？

Question

我有以下疑问：

SELECT cp.ID_Case
FROM dbo.CaseParty cp (NOLOCK)
JOIN dbo.Client cli (NOLOCK) ON CASE
     WHEN cli.ClientType = 'atty' AND cp.ID_ClientAttorney = cli.ID_Client THEN 1
     WHEN cli.ClientType = 'adj' AND cp.ID_ClientAdjuster = cli.ID_Client THEN 1
     ELSE 0
     END = 1
WHERE cli.ID_Client = @ID_Client

当我运行它时，执行计划会对表 CaseParty 的主键索引执行聚集索引扫描。 该表中有大约 700k 行，因此查询需要大量时间。 我承认需要

CASE

声明的连接不太理想，但这就是我必须处理的。

我尝试过创建各种索引，但它只是不会使用它们：

CREATE INDEX IX_CaseParty_ClientAttorneyAdjuster ON dbo.CaseParty (ID_ClientAttorney, ID_ClientAdjuster);
CREATE INDEX IX_CaseParty_ClientAttorney ON dbo.CaseParty (ID_ClientAttorney);
CREATE INDEX IX_CaseParty_ClientAdjuster ON dbo.CaseParty (ID_ClientAdjuster);

我还尝试将

CASE

连接更改为

OR

（下面的示例），但它没有任何改变。

SELECT cp.ID_Case
FROM dbo.CaseParty cp (NOLOCK)
JOIN dbo.Client cli (NOLOCK) 
    ON (cli.ClientType = 'atty' AND cp.ID_ClientAttorney = cli.ID_Client)
    OR (cli.ClientType = 'adj' AND cp.ID_ClientAdjuster = cli.ID_Client)
WHERE cli.ID_Client = @ID_Client

我做错了什么？

Answer 1

选择 cp.ID_Case 来自 dbo.CaseParty cp (NOLOCK) JOIN dbo.Client cli_atty (NOLOCK) ON cp.ID_ClientAttorney = cli_atty.ID_Client AND cli_atty.ClientType = 'atty' 其中 cli_atty.ID_Client = @ID_Client

联盟

选择 cp.ID_Case 来自 dbo.CaseParty cp (NOLOCK) JOIN dbo.Client cli_adj (NOLOCK) ON cp.ID_ClientAdjuster = cli_adj.ID_Client AND cli_adj.ClientType = 'adj' 其中 cli_adj.ID_Client = @ID_Client