[英]WHERE_IN query with a composite key?
假設我有一個包含兩部分組成的組合鍵和4條記錄的表,如下所示:
KEY_PART_1 KEY_PART_2
A 1
B 1
C 2
C 3
我想編寫一些動態SQL,以使用“ WHERE IN”子句僅選擇記錄B,1和C,2, 而不選擇A,1或C,3。
沒有臨時表,有什么方法可以做到這一點嗎?
沒關系,但是我們目前正在使用Oracle,並希望盡快遷移到PostgreSQL。
此語法適用於Oracle和PostgreSQL:
SELECT *
FROM table_name
WHERE (key_part_1, key_part_2) IN ( ('B',1), ('C',2) );
在@Justin Cave的回答之后,這是一個小測試用例,用於說明Oracle將對以下過濾謂詞執行INDEX RANGE SCAN,然后執行INLIST ITERATOR :
WHERE (key_part_1, key_part_2) IN ( ('B',1), ('C',2) )
設定
SQL> CREATE TABLE t(key1 VARCHAR2(1), key2 NUMBER);
Table created.
SQL>
SQL> INSERT INTO t VALUES('A', 1);
1 row created.
SQL> INSERT INTO t VALUES('B', 1);
1 row created.
SQL> INSERT INTO t VALUES('C', 2);
1 row created.
SQL> INSERT INTO t VALUES('C', 3);
1 row created.
SQL>
SQL> COMMIT;
Commit complete.
SQL>
key1和key2的 復合索引 :
SQL> CREATE INDEX t_idx ON t(key1, key2);
Index created.
SQL>
收集統計信息:
SQL> EXEC DBMS_STATS.gather_table_stats('LALIT', 'T');
PL/SQL procedure successfully completed.
SQL>
執行查詢:
SQL> SELECT * FROM t
2 WHERE (key1, key2) IN ( ('B',1), ('C',2) );
K KEY2
- ----------
B 1
C 2
SQL>
因此,它給出了正確的輸出。
讓我們看一下解釋計划 :
案例#1鍵值對的索引順序相同。 領先的關鍵。
SQL> SELECT * FROM TABLE(dbms_xplan.display);
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 2301620486
---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 2 | 10 | 1 (0)| 00:00:01 |
| 1 | INLIST ITERATOR | | | | | |
|* 2 | INDEX RANGE SCAN| T_IDX | 2 | 10 | 1 (0)| 00:00:01 |
---------------------------------------------------------------------------
Predicate Information (identified by operation id):
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
---------------------------------------------------
2 - access(("KEY1"='B' AND "KEY2"=1 OR "KEY1"='C' AND "KEY2"=2))
14 rows selected.
案例#2索引相反的鍵值對。 前導鍵反向。
SQL> EXPLAIN PLAN FOR SELECT * FROM t
2 WHERE (key2, key1) IN ( (1, 'B'), (2, 'C') );
Explained.
SQL>
SQL> SELECT * FROM TABLE(dbms_xplan.display);
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 2301620486
---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 2 | 10 | 1 (0)| 00:00:01 |
| 1 | INLIST ITERATOR | | | | | |
|* 2 | INDEX RANGE SCAN| T_IDX | 2 | 10 | 1 (0)| 00:00:01 |
---------------------------------------------------------------------------
Predicate Information (identified by operation id):
PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
---------------------------------------------------
2 - access(("KEY1"='B' AND "KEY2"=1 OR "KEY1"='C' AND "KEY2"=2))
14 rows selected.
在這兩種情況下, Oracle都使用index 。
我不確定,但我認為您想要這樣的東西,幾乎適用於所有RDBMS:
select KEY_PART_1, KEY_PART_2 from your_table where KEY_PART_1='B' and KEY_PART_2 = '1'
UNION
select KEY_PART_1, KEY_PART_2 from your_table where KEY_PART_1='C' and KEY_PART_2 = '2'
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