應該爲更快的查詢創建多少個索引

Question

我的對象模型在下面給出，並且希望您輸入關於爲更快的查詢響應（在h2，mysql上）創建的索引數量。假設和問題在下面的模型中給出。

@Entity 
@Table(name = "user") 
public class User { 

    @Id 
    @GeneratedValue(strategy = IDENTITY) 
    @Column(name = "id", unique = true, nullable = false, insertable = false, updatable = false) 
    private Integer id; 

    @ManyToOne(fetch = FetchType.LAZY) 
    @ForeignKey(name = "fk_user_org_id") 
    @Index(name = "idx_user_org_id") 
    @JoinColumn(name = "org_id", nullable = false, referencedColumnName = "id") 
    @NotNull 
    private Organization organization; 

    @ManyToOne(fetch = FetchType.LAZY) 
    @ForeignKey(name = "fk_user_year_id") 
    @Index(name = "idx_user_year_id") 
    @JoinColumn(name = "year", nullable = false, referencedColumnName = "id") 
    @NotNull 
    private Year year; 

    @ManyToOne(fetch = FetchType.LAZY) 
    @ForeignKey(name = "fk_user_created_by") 
    @Index(name = "idx_user_created_by") 
    @JoinColumn(name = "created_by", nullable = false, referencedColumnName = "id") 
    @NotNull 
    private User createdBy; 

    @Column(name = "name", nullable = false) 
    private String name; 

    @Column(name = "desc") 
    private String desc; 

    @Column(name = "is_system", length = LEN_1) 
    @Type(type = "org.hibernate.type.YesNoType") 
    private boolean isSystem = false; 

    @Column(name = "user_type", nullable = false) 
    private UserType userType; 

    @Column(name = "status", nullable = false) 
    @NotNull 
    private Status status; 

} 

我們的計劃是用的，而不是單一的列索引多列索引（即基於創建索引user_idx（組織，一年，isSystem，狀態，用戶類型，createdBy））。假設我有這個索引，我會針對下面列出的查詢得到優化的響應。

1. select * from user where organization = 1 and year = 2010;
2. select * from user where organization = 1 and year = 2010 and isSytem = true or false; （即系統用戶或應用程序定義的用戶）
3. select * from user where organization = 1 and year = 2010 and isSytem = false and userType = Manager（即所有管理員）
4. select * from user where organization = 1 and year = 2010且isSytem = false和userType = Employee（即所有員工）
5. select * from user where organization = 1 and year = 2010 and isSytem = false and userType = Manager and status = ACTIVE（即活動用戶）

6. select * from user where organization = 1 and year = 2010 and createdBy ='Sam'or'Joe' [6]是否需要一個不同的多列索引，由上面的3列組成？

7. 由於我們根據原始假設創建了多列索引，我可以安全地刪除模型中當前定義的各個索引（idx_user_org_id，idx_user_year_id，idx_user_created_by）嗎？

Answer 1

您應切換列的順序在索引：

(organization, year, isSystem, userType, status, createdBy) 

這使得它可以更好地服務於這兩個查詢：

select * from user where organization=1 and year=2010 and isSystem=false and userType=Manager 
select * from user where organization=1 and year=2010 and isSystem=false and userType=Employee 

確實[6]需要一個不同的多列索引，由以上三列組成？

它並不需要一個新指數 - 它可以使用現有的一個，但在一個不太有效的方式 - 只有前兩列將被使用。儘管爲這個查詢添加一個新的索引看起來不錯。

我可以安全地刪除各個索引

是。您應該刪除未使用的索引，否則它們將佔用磁盤空間並放慢表格修改速度，但不提供任何好處。