统计信息不准导致执行计划出错跑不出结果，优化后只要1分钟-mysql教程-PHP中文網

一天查看数据库长会话，发现1个sql跑得很慢，1个多小时不出结果，花了点时间把它给优化了。优化前： SELECT 20131023, A2.ORG_ID, COUNT(DISTINCT NLSSORT(CASE A2.RES_TYPE WHEN DP THEN A2.RES_CODE END, nls_sort=BINARY)), COUNT(DISTINCT NLSSORT(CASE

一天查看数据库长会话，发现1个sql跑得很慢，1个多小时不出结果，花了点时间把它给优化了。

优化前：

SELECT 20131023,
       "A2"."ORG_ID",
       COUNT(DISTINCT NLSSORT(CASE "A2"."RES_TYPE"
                       WHEN &#39;DP&#39; THEN
                        "A2"."RES_CODE"
                     END,
                     &#39;nls_sort=&#39;&#39;BINARY&#39;&#39;&#39;)),
       COUNT(DISTINCT NLSSORT(CASE "A2"."RES_TYPE"
                       WHEN &#39;BOX&#39; THEN
                        "A2"."RES_CODE"
                     END,
                     &#39;nls_sort=&#39;&#39;BINARY&#39;&#39;&#39;)),
       COUNT(DISTINCT NLSSORT(CASE "A2"."RES_TYPE"
                       WHEN &#39;ONU&#39; THEN
                        "A2"."RES_CODE"
                     END,
                     &#39;nls_sort=&#39;&#39;BINARY&#39;&#39;&#39;)),
       COUNT(DISTINCT NLSSORT(CASE "A2"."RES_TYPE"
                       WHEN &#39;OBD&#39; THEN
                        "A2"."RES_CODE"
                     END,
                     &#39;nls_sort=&#39;&#39;BINARY&#39;&#39;&#39;)),
       COUNT(DISTINCT NLSSORT(CASE
                       WHEN ("A1"."CON_TYPE" = &#39;001&#39; AND "A2"."RES_TYPE" = &#39;DP&#39;) THEN
                        "A1"."RES_ID"
                     END,
                     &#39;nls_sort=&#39;&#39;BINARY&#39;&#39;&#39;)),
       COUNT(DISTINCT NLSSORT(CASE
                       WHEN ("A1"."CON_TYPE" = &#39;002&#39; AND "A2"."RES_TYPE" = &#39;BOX&#39;) THEN
                        "A1"."RES_ID"
                     END,
                     &#39;nls_sort=&#39;&#39;BINARY&#39;&#39;&#39;)),
       COUNT(DISTINCT NLSSORT(CASE
                       WHEN ("A1"."CON_TYPE" = &#39;0011&#39; AND "A2"."RES_TYPE" = &#39;ONU&#39;) THEN
                        "A1"."RES_ID"
                     END,
                     &#39;nls_sort=&#39;&#39;BINARY&#39;&#39;&#39;)),
       COUNT(DISTINCT NLSSORT(CASE
                       WHEN ("A1"."CON_TYPE" = &#39;0022&#39; AND "A2"."RES_TYPE" = &#39;OBD&#39;) THEN
                        "A1"."RES_ID"
                     END,
                     &#39;nls_sort=&#39;&#39;BINARY&#39;&#39;&#39;))
  FROM "CRM_SZ"."AAA" "A2",
       "CRM_SZ"."BBB" "A1"
 WHERE "A1"."RES_ID"(+) = "A2"."RES_CODE"
 GROUP BY "A2"."ORG_ID"

执行计划：
Plan hash value: 2627707252
 
---------------------------------------------------------------------------------------
| Id  | Operation           | Name            | Rows  | Bytes | Cost (%CPU)| Time     |
---------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT    |                 |     1 |  1065 |     3  (34)| 00:00:01 |
|   1 |  SORT GROUP BY      |                 |     1 |  1065 |     3  (34)| 00:00:01 |
|   2 |   NESTED LOOPS OUTER|                 |     1 |  1065 |     2   (0)| 00:00:01 |
|   3 |    TABLE ACCESS FULL| AAA             |     1 |   539 |     2   (0)| 00:00:01 |
|*  4 |    INDEX FULL SCAN  | IX_MO_CON_VALUE |     1 |   526 |     0   (0)| 00:00:01 |
---------------------------------------------------------------------------------------
 
Predicate Information (identified by operation id):
---------------------------------------------------
 
   4 - access("A1"."RES_ID"(+)="A2"."RES_CODE")
       filter("A1"."RES_ID"(+)="A2"."RES_CODE")

登入後複製

cbo估算错了，rows全是1，导致走nl
手工count了一把：
select count(*) from "CRM_SZ"."AAA" ;--1365564
select count(*) from "CRM_SZ"."BBB";--119949
走nl那岂不是sb啦。

第一次优化后：

SELECT/*+use_hash(A1,A2) swap_join_inputs(A1)*/20131023,
       "A2"."ORG_ID",
       COUNT(DISTINCT NLSSORT(CASE "A2"."RES_TYPE"
                       WHEN &#39;DP&#39; THEN
                        "A2"."RES_CODE"
                     END,
                     &#39;nls_sort=&#39;&#39;BINARY&#39;&#39;&#39;)),
       COUNT(DISTINCT NLSSORT(CASE "A2"."RES_TYPE"
                       WHEN &#39;BOX&#39; THEN
                        "A2"."RES_CODE"
                     END,
                     &#39;nls_sort=&#39;&#39;BINARY&#39;&#39;&#39;)),
       COUNT(DISTINCT NLSSORT(CASE "A2"."RES_TYPE"
                       WHEN &#39;ONU&#39; THEN
                        "A2"."RES_CODE"
                     END,
                     &#39;nls_sort=&#39;&#39;BINARY&#39;&#39;&#39;)),
       COUNT(DISTINCT NLSSORT(CASE "A2"."RES_TYPE"
                       WHEN &#39;OBD&#39; THEN
                        "A2"."RES_CODE"
                     END,
                     &#39;nls_sort=&#39;&#39;BINARY&#39;&#39;&#39;)),
       COUNT(DISTINCT NLSSORT(CASE
                       WHEN ("A1"."CON_TYPE" = &#39;001&#39; AND "A2"."RES_TYPE" = &#39;DP&#39;) THEN
                        "A1"."RES_ID"
                     END,
                     &#39;nls_sort=&#39;&#39;BINARY&#39;&#39;&#39;)),
       COUNT(DISTINCT NLSSORT(CASE
                       WHEN ("A1"."CON_TYPE" = &#39;002&#39; AND "A2"."RES_TYPE" = &#39;BOX&#39;) THEN
                        "A1"."RES_ID"
                     END,
                     &#39;nls_sort=&#39;&#39;BINARY&#39;&#39;&#39;)),
       COUNT(DISTINCT NLSSORT(CASE
                       WHEN ("A1"."CON_TYPE" = &#39;0011&#39; AND "A2"."RES_TYPE" = &#39;ONU&#39;) THEN
                        "A1"."RES_ID"
                     END,
                     &#39;nls_sort=&#39;&#39;BINARY&#39;&#39;&#39;)),
       COUNT(DISTINCT NLSSORT(CASE
                       WHEN ("A1"."CON_TYPE" = &#39;0022&#39; AND "A2"."RES_TYPE" = &#39;OBD&#39;) THEN
                        "A1"."RES_ID"
                     END,
                     &#39;nls_sort=&#39;&#39;BINARY&#39;&#39;&#39;))
  FROM "CRM_SZ"."AAA"        "A2",
       "CRM_SZ"."BBB" "A1"
 WHERE "A1"."RES_ID"(+) = "A2"."RES_CODE"
 GROUP BY "A2"."ORG_ID"

63 rows selected.

Elapsed: 00:00:47.64

Execution Plan
----------------------------------------------------------
Plan hash value: 3074972763

------------------------------------------------------------------------------------------
| Id  | Operation              | Name            | Rows  | Bytes | Cost (%CPU)| Time     |
------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT       |                 |     1 |  1065 |     4  (50)| 00:00:01 |
|   1 |  SORT GROUP BY         |                 |     1 |  1065 |     4  (50)| 00:00:01 |
|*  2 |   HASH JOIN RIGHT OUTER|                 |     1 |  1065 |     3  (34)| 00:00:01 |
|   3 |    INDEX FULL SCAN     | IX_MO_CON_VALUE |     1 |   526 |     0   (0)| 00:00:01 |
|   4 |    TABLE ACCESS FULL   | AAA             |     1 |   539 |     2   (0)| 00:00:01 |
------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

   2 - access("A1"."RES_ID"(+)="A2"."RES_CODE")

Statistics
----------------------------------------------------------
       1065  recursive calls
          3  db block gets
      13375  consistent gets
      16369  physical reads
          0  redo size
       4862  bytes sent via SQL*Net to client
        791  bytes received via SQL*Net from client
          6  SQL*Net roundtrips to/from client
         12  sorts (memory)
          1  sorts (disk)
         63  rows processed

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第二次优化后：

SELECT/*+use_hash(A1,A2) full(A1) full(A2) parallel(A1,5) parallel(A2,5) swap_join_inputs(A1)*/20131023,
       "A2"."ORG_ID",
       COUNT(DISTINCT NLSSORT(CASE "A2"."RES_TYPE"
                       WHEN &#39;DP&#39; THEN
                        "A2"."RES_CODE"
                     END,
                     &#39;nls_sort=&#39;&#39;BINARY&#39;&#39;&#39;)),
       COUNT(DISTINCT NLSSORT(CASE "A2"."RES_TYPE"
                       WHEN &#39;BOX&#39; THEN
                        "A2"."RES_CODE"
                     END,
                     &#39;nls_sort=&#39;&#39;BINARY&#39;&#39;&#39;)),
       COUNT(DISTINCT NLSSORT(CASE "A2"."RES_TYPE"
                       WHEN &#39;ONU&#39; THEN
                        "A2"."RES_CODE"
                     END,
                     &#39;nls_sort=&#39;&#39;BINARY&#39;&#39;&#39;)),
       COUNT(DISTINCT NLSSORT(CASE "A2"."RES_TYPE"
                       WHEN &#39;OBD&#39; THEN
                        "A2"."RES_CODE"
                     END,
                     &#39;nls_sort=&#39;&#39;BINARY&#39;&#39;&#39;)),
       COUNT(DISTINCT NLSSORT(CASE
                       WHEN ("A1"."CON_TYPE" = &#39;001&#39; AND "A2"."RES_TYPE" = &#39;DP&#39;) THEN
                        "A1"."RES_ID"
                     END,
                     &#39;nls_sort=&#39;&#39;BINARY&#39;&#39;&#39;)),
       COUNT(DISTINCT NLSSORT(CASE
                       WHEN ("A1"."CON_TYPE" = &#39;002&#39; AND "A2"."RES_TYPE" = &#39;BOX&#39;) THEN
                        "A1"."RES_ID"
                     END,
                     &#39;nls_sort=&#39;&#39;BINARY&#39;&#39;&#39;)),
       COUNT(DISTINCT NLSSORT(CASE
                       WHEN ("A1"."CON_TYPE" = &#39;0011&#39; AND "A2"."RES_TYPE" = &#39;ONU&#39;) THEN
                        "A1"."RES_ID"
                     END,
                     &#39;nls_sort=&#39;&#39;BINARY&#39;&#39;&#39;)),
       COUNT(DISTINCT NLSSORT(CASE
                       WHEN ("A1"."CON_TYPE" = &#39;0022&#39; AND "A2"."RES_TYPE" = &#39;OBD&#39;) THEN
                        "A1"."RES_ID"
                     END,
                     &#39;nls_sort=&#39;&#39;BINARY&#39;&#39;&#39;))
  FROM "CRM_SZ"."AAA"        "A2",
       "CRM_SZ"."BBB" "A1"
 WHERE "A1"."RES_ID"(+) = "A2"."RES_CODE"
 GROUP BY "A2"."ORG_ID";

63 rows selected.

Elapsed: 00:00:10.21

Execution Plan
----------------------------------------------------------
Plan hash value: 4044842257

-------------------------------------------------------------------------------------------------------------------------------------
| Id  | Operation                      | Name                  | Rows  | Bytes | Cost (%CPU)| Time     |    TQ  |IN-OUT| PQ Distrib |
-------------------------------------------------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT               |                       |     1 |  1065 |     6  (34)| 00:00:01 |        |      |            |
|   1 |  PX COORDINATOR                |                       |       |       |            |          |        |      |            |
|   2 |   PX SEND QC (RANDOM)          | :TQ10004              |     1 |  1065 |     6  (34)| 00:00:01 |  Q1,04 | P->S | QC (RAND)  |
|   3 |    SORT GROUP BY               |                       |     1 |  1065 |     6  (34)| 00:00:01 |  Q1,04 | PCWP |            |
|   4 |     PX RECEIVE                 |                       |     1 |  1065 |     6  (34)| 00:00:01 |  Q1,04 | PCWP |            |
|   5 |      PX SEND HASH              | :TQ10003              |     1 |  1065 |     6  (34)| 00:00:01 |  Q1,03 | P->P | HASH       |
|   6 |       SORT GROUP BY            |                       |     1 |  1065 |     6  (34)| 00:00:01 |  Q1,03 | PCWP |            |
|   7 |        PX RECEIVE              |                       |     1 |  1065 |     6  (34)| 00:00:01 |  Q1,03 | PCWP |            |
|   8 |         PX SEND HASH           | :TQ10002              |     1 |  1065 |     6  (34)| 00:00:01 |  Q1,02 | P->P | HASH       |
|   9 |          SORT GROUP BY         |                       |     1 |  1065 |     6  (34)| 00:00:01 |  Q1,02 | PCWP |            |
|* 10 |           HASH JOIN RIGHT OUTER|                       |     1 |  1065 |     5  (20)| 00:00:01 |  Q1,02 | PCWP |            |
|  11 |            PX RECEIVE          |                       |     1 |   526 |     2   (0)| 00:00:01 |  Q1,02 | PCWP |            |
|  12 |             PX SEND HASH       | :TQ10000              |     1 |   526 |     2   (0)| 00:00:01 |  Q1,00 | P->P | HASH       |
|  13 |              PX BLOCK ITERATOR |                       |     1 |   526 |     2   (0)| 00:00:01 |  Q1,00 | PCWC |            |
|  14 |               TABLE ACCESS FULL| BBB                   |     1 |   526 |     2   (0)| 00:00:01 |  Q1,00 | PCWP |            |
|  15 |            PX RECEIVE          |                       |     1 |   539 |     2   (0)| 00:00:01 |  Q1,02 | PCWP |            |
|  16 |             PX SEND HASH       | :TQ10001              |     1 |   539 |     2   (0)| 00:00:01 |  Q1,01 | P->P | HASH       |
|  17 |              PX BLOCK ITERATOR |                       |     1 |   539 |     2   (0)| 00:00:01 |  Q1,01 | PCWC |            |
|  18 |               TABLE ACCESS FULL| AAA                   |     1 |   539 |     2   (0)| 00:00:01 |  Q1,01 | PCWP |            |
-------------------------------------------------------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------

  10 - access("A1"."RES_ID"(+)="A2"."RES_CODE")


Statistics
----------------------------------------------------------
        585  recursive calls
          4  db block gets
      14267  consistent gets
      13126  physical reads
        808  redo size
       4888  bytes sent via SQL*Net to client
        840  bytes received via SQL*Net from client
          6  SQL*Net roundtrips to/from client
         23  sorts (memory)
          0  sorts (disk)
         63  rows processed

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优化前，执行计划走了nl，1个多小时查不出结果
第一次优化后，首次00:00:47.64可以出结果
第二次优化后，首次00:00:10.21出结果，重复执行（有缓存）的情况下3s出结果。