如何提高Oracle SQL中两个SCD2表的JOIN性能

Question

I have two tables, both using valid to and valid from logic. Table 1 looks like this:

ID | VALID_FROM | VALID_TO 
1  | 01.01.2000 | 04.01.2000
1  | 04.01.2000 | 16.01.2000
1  | 16.01.2000 | 17.01.2000
1  | 17.01.2000 | 19.01.2000
2  | 03.02.2001 | 04.04.2001
2  | 04.04.2001 | 14.03.2001
2  | 14.04.2001 | 18.03.2001

while table 2 looks like this:

ID | VAR | VALID_FROM | VALID_TO 
1  |  3  | 01.01.2000 | 17.01.2000
1  |  2  | 17.01.2000 | 19.01.2000
2  |  4  | 03.02.2001 | 14.03.2001

• Table 1 has 132,195,791 rows and table 2 has 16,964,846.
• The valid from and valid to date of any observation in table 1 is within one or more valid from to valid to windows shown in table 2.
• I created primary keys for both of them over ID and VALID_FROM
• I want to do an inner join like:

    select t1.*, 
           t2.var 
      from t1 t1
inner join t2 t2
        on t1.id = t2.id
       and t1.valid_from >= t2.valid_from
       and t1.valid_to <= t2.valid_to;

This join is really slow. I ran it half a day without any success. What can I do to increase performance in this particular case? Please note that I also want to left join the resulting table in later stages. Any help is highly appreciated.

EDIT

Obviously, the information I gave was less then generally desired here on the platform.

• I use Oracle Database 12c Enterprise Edition
• The example I gave was illustrative for the bigger problem at hand. I am concerned with joining information from different tables with different valid_from / valid_to dates. For this I created a grid first with the distinct values in the valid_from and valid_to variables of all the relevant tables. This grid is what I refer here to as table 1.
• Results from the execution plan (I adjusted the column and table names to meet the terminology used in my illustrative example):

    --------------------------------------------------------------------------------------
    | Id  | Operation          | Name    | Rows  | Bytes |TempSpc| Cost (%CPU)| Time     |
    --------------------------------------------------------------------------------------
    |   0 | SELECT STATEMENT   |         |   465M|    23G|       |   435K  (3)| 00:00:18 |
    |*  1 |  HASH JOIN         |         |   465M|    23G|   695M|   435K  (3)| 00:00:18 |
    |   2 |   TABLE ACCESS FULL| TABLE2 |    16M|   501M|       | 22961   (2)| 00:00:01 |
    |   3 |   TABLE ACCESS FULL| TABLE1 |   132M|  3025M|       |   145K  (2)| 00:00:06 |
    --------------------------------------------------------------------------------------

    Query Block Name / Object Alias (identified by operation id):
    -------------------------------------------------------------

       1 - SEL$58A6D7F6
       2 - SEL$58A6D7F6 / T2@SEL$1
       3 - SEL$58A6D7F6 / T1@SEL$1

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

       1 - access("T1"."ID"="T2"."ID")
           filter("T1"."VALID_TO"<="T2"."VALID_TO" AND 
                  "T1"."VALID_FROM">="T2"."VALID_FROM")

    Column Projection Information (identified by operation id):
    -----------------------------------------------------------

       1 - (#keys=1) "T2"."ID"[VARCHAR2,20], 
           "T1"."ID"[VARCHAR2,20], "T1"."VALID_TO"[DATE,7], 
           "T2"."VAR"[VARCHAR2,20], "T2"."VALID_FROM"[DATE,7], 
           "T2"."VALID_TO"[DATE,7], "T1"."ID"[VARCHAR2,20], 
           "T1"."VALID_FROM"[DATE,7], "T1"."VALID_TO"[DATE,7], "T1"."VALID_FROM"[DATE,7]
       2 - "T2"."ID"[VARCHAR2,20], 
           "T2"."VAR"[VARCHAR2,20], "T2"."VALID_FROM"[DATE,7], 
           "T2"."VALID_TO"[DATE,7]
       3 - "T1"."ID"[VARCHAR2,20], "T1"."VALID_FROM"[DATE,7], 
           "T1"."VALID_TO"[DATE,7]

    Note
    -----
       - this is an adaptive plan

Answer 1

A good practice is to ask first: what is expected the query will return?

Base on your WHERE predicate is seems you are interested on all versions from table2 that are included in the validity interval of table1. This may be intention, but more common you need all versions that intersect between the tables.

The second aspect is, do you need to see few first rows or all rows from the join.

If you only want to see few results, simple add AND t1.ID = nnnn to the WHERE clause to limit to some sample ID . If you have proper indexes (and tehre are no expreme lot of rows with this ID), you will get the result quick as NESTED LOOP join will kick in.

To perform the the full result, you must consider all rows from both tables. No index will help you to select all rows from a table - here is the FULL TABLE SCAN the best option.

To join the large row sets the best approach is HASH JOIN . NESTED LOOPS (which you probably use now) are quick to join few rows, but hangs on large row sets.

The smaller table (table2) is red in memory (hopefully) as a hash table. The larger table (table1) is probed against this hash table toperform the join.

This is the execution plan you should look for

-----------------------------------------------------------------------------------
| Id  | Operation          | Name | Rows  | Bytes |TempSpc| Cost (%CPU)| Time     |
-----------------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |    10T|   399T|       |   190M(100)| 02:03:47 |
|*  1 |  HASH JOIN         |      |    10T|   399T|   550M|   190M(100)| 02:03:47 |
|   2 |   TABLE ACCESS FULL| SCD2 |    16M|   355M|       |    39  (93)| 00:00:01 |
|   3 |   TABLE ACCESS FULL| SCD1 |   132M|  2395M|       |   211  (99)| 00:00:01 |
-----------------------------------------------------------------------------------

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

   1 - access("T1"."ID"="T2"."ID")
       filter("T1"."VALID_FROM">="T2"."VALID_FROM" AND 
              "T1"."VALID_TO"<="T2"."VALID_TO")

Provided you are on an enterprise database this should pass you from days to hours . Further you can deploy parallel option to get additional speed up.

Good luck!