3

你们能否请查看以下对 Oracle DB 的查询并指出问题所在：

SELECT t1.name FROM t1, t2 WHERE t1.id = t2.id AND t2.empno IN (1, 2, 3, …, 200)

查询统计：

  • 耗时：10.53 秒。

指数：

  • t2.empno被索引。

  • t1.id被索引。

  • t2.id被索引。

更新

上面的查询只是我使用的查询的一个示例副本。下面以更真实的形式

解释计划 解释计划

询问：

SELECT 
    PRODUCT_REPRESENTATION_SK 
FROM 
    Product_Representation pr 
    , Design_Object do
    , Files files  
    ,EPS_STATUS epsStatus 
    ,EPS_ERROR_CODES epsError
    ,VIEW_TYPE viewTable  
WHERE  
    pr.DESIGN_OBJECT_SK = do.DESIGN_OBJECT_SK 
    AND  pr.LAYER_NAME !='Layer 0' 
    AND  epsStatus.EPS_STATUS_SK = pr.EPS_STATUS  
    AND epsError.EPS_ERROR_CODE = pr.EPS_ERROR_CODE 
    AND viewTable.VIEW_TYPE_ID = pr.VIEW_TYPE_ID 
    AND  files.pim_id = do.PIM_ID 
    AND  do.DESIGN_OBJECT_ID IN
        (
147086,149924,140458,135068,145197,134774,141837,138568,141731,138772,143769,141739,149113,148809,141072,141732,143974,147076,143972,141078,141925,134643,139701,141729,147078,139120,137097,147072,138261,149700,149701,139127,147070,149702,136766,146829,135762,140155,148459,138061,138762.............................................  200 such numbers
        )

索引列：

pr.DESIGN_OBJECT_SK
do.DESIGN_OBJECT_SK
do.DESIGN_OBJECT_ID
files.pim_id

桌子

TABLE "PIM"."DESIGN_OBJECT" 
(   
"DESIGN_OBJECT_SK" NUMBER(*,0) NOT NULL ENABLE, 
"PIM_ID" NUMBER(*,0) NOT NULL ENABLE, 
"DESIGN_OBJECT_TYPE_SK" NUMBER(*,0) NOT NULL ENABLE, 
"DESIGN_OBJECT_ID" VARCHAR2(40 BYTE) NOT NULL ENABLE, 
"DIVISION_CD" NUMBER(*,0), 
"STAT_IND" NUMBER(*,0) NOT NULL ENABLE, 
"STAT_CHNG_TMST" TIMESTAMP (6), 
"CRTD_BY" VARCHAR2(45 BYTE), 
"CRT_TMST" TIMESTAMP (6), 
"MDFD_BY" VARCHAR2(45 BYTE), 
"CHNG_TMST" TIMESTAMP (6), 
"UPDATE_CNT" NUMBER(*,0), 
"GENDER" VARCHAR2(1 BYTE), 

 PRIMARY KEY ("DESIGN_OBJECT_SK")
)
TABLESPACE "PIM"  ENABLE, 

FOREIGN KEY ("DESIGN_OBJECT_TYPE_SK")
    REFERENCES "PIM"."DESIGN_OBJECT_TYPE" ("DESIGN_OBJECT_TYPE_SK")
        ON DELETE CASCADE ENABLE, 

FOREIGN KEY ("PIM_ID")
    REFERENCES "PIM"."FILES" ("PIM_ID")
        ON DELETE CASCADE ENABLE

)

表 2

CREATE TABLE "PIM"."PRODUCT_REPRESENTATION" 
(
"PRODUCT_REPRESENTATION_SK" NUMBER(*,0) NOT NULL ENABLE, 
"DESIGN_OBJECT_SK" NUMBER(*,0) NOT NULL ENABLE, 
"VIEW_TYPE_ID" NUMBER(*,0) NOT NULL ENABLE, 
"LAYER_NAME" VARCHAR2(255 BYTE), 
"STAT_IND" NUMBER(*,0) NOT NULL ENABLE, 
"STAT_CHNG_TMST" TIMESTAMP (6), 
"CRTD_BY" VARCHAR2(45 BYTE), 
"CRT_TMST" TIMESTAMP (6), 
"MDFD_BY" VARCHAR2(45 BYTE), 
"CHNG_TMST" TIMESTAMP (6), 
"UPDATE_CNT" NUMBER(*,0), 
"EPS_STATUS" VARCHAR2(30 BYTE) NOT NULL ENABLE, 
"EPS_GENERATED_TIME" TIMESTAMP (6), 
"EPS_ERROR_CODE" NUMBER, 
"EPS_ERROR_DETAILS" VARCHAR2(500 BYTE), 
"DEEPSERVER_ASSET_LAYER_ID" VARCHAR2(255 BYTE), 
"PRODUCT_REPRESENTATION_LOC" VARCHAR2(255 BYTE), 

 PRIMARY KEY ("PRODUCT_REPRESENTATION_SK")
)
TABLESPACE "PIM"  ENABLE, 

FOREIGN KEY ("DESIGN_OBJECT_SK")
    REFERENCES "PIM"."DESIGN_OBJECT" ("DESIGN_OBJECT_SK") 
        ON DELETE CASCADE ENABLE, 
FOREIGN KEY ("VIEW_TYPE_ID")
    REFERENCES "PIM"."VIEW_TYPE" ("VIEW_TYPE_ID")
        ON DELETE CASCADE ENABLE, 

CONSTRAINT "EPS_ERROR_CODE_FK"
FOREIGN KEY ("EPS_ERROR_CODE")
     REFERENCES "PIM"."EPS_ERROR_CODES" ("EPS_ERROR_CODE") 
        ON DELETE CASCADE ENABLE, 
CONSTRAINT "EPS_STATUS_FK" 
FOREIGN KEY ("EPS_STATUS")
    REFERENCES "PIM"."EPS_STATUS" ("EPS_STATUS_SK") 
        ON DELETE CASCADE ENABLE
)
4

3 回答 3

8

让我们暂时忘记这个empno BETWEEN 1 and 200建议并假设你有t2.empno IN (3,7,...,5209)（200 个条目）。

您还可以将查询（这是一个隐藏的 JOIN 查询）写入非等效EXISTS 查询，该查询将显示相同的结果（但可能行更少）并且应该比 JOIN 更快：

SELECT
    t1.name
FROM
    t1
WHERE EXISTS
      ( SELECT *
        FROM t2
        WHERE t2.id = t1.id
          AND t2.empno IN (3,7,...,5209)
      )

（疯狂猜测）

另一方面，如果不是，但t2.empno IN (3,7,...,5209)您正在使用 MySQL，那么这就是您的问题的根源（众所周知，MySQL 无法以最佳方式处理）。因此，您可以将查询更改为：t2.empno IN (SELECT tx.empno FROM tx WHERE someConditions) field IN (SELECT f FROM x)

SELECT
    t1.name
FROM
    t1
  JOIN t2
    ON t2.id = t2.id
  JOIN tx
    ON tx.empno = t2.empno
WHERE
    someConditions

甚至：

SELECT
    t1.name
FROM
    t1
WHERE EXISTS
      ( SELECT *
        FROM t2
          JOIN tx
            ON tx.empno = t2.empno
        WHERE t2.id = t1.id
          AND someConditions
      )
于 2011-08-11T15:50:31.993 回答
7

错误的第一件事是使用隐式连接语法。那是一个 SQL 反模式。

如果您在 IN 子句中有一个大列表，您是否尝试过将它们放在一个表中并使用连接？

什么数据库？您是否查看过您的解释计划或执行计划以了解减速在哪里？

于 2011-08-11T15:23:52.800 回答
3

不要使用交叉连接。

尝试这个

SELECT
    t1.name
FROM
    t1
JOIN t2
    ON t2.id = t1.id
WHERE
    t2.empno IN (1,...,200)

编辑：编辑后，看到笛卡尔积中的多个表，使用正确的JOIN语法可能非常重要。

于 2011-08-11T15:23:29.697 回答