共计 3961 个字符，预计需要花费 10 分钟才能阅读完成。
这篇文章主要讲解了“Oracle 与 PostgreSQL 的 NULL 和索引使用区别是什么”，文中的讲解内容简单清晰，易于学习与理解，下面请大家跟着丸趣 TV 小编的思路慢慢深入，一起来研究和学习“Oracle 与 PostgreSQL 的 NULL 和索引使用区别是什么”吧！
Oracle 在创建索引时, 不会存储 NULL 值, 而 PostgreSQL 在创建索引时则会存储 NULL 值. 在查询时, 如使用 Column is null 这样的条件查询,Oracle 不会使用索引而 PostgreSQL 则会使用索引.
Oracle
插入数据,200w 多行的数据, 然后插入一行值为 null 的数据.
TEST-orcl@DESKTOP-V430TU3 create table tbl1(id int);
Table created.
TEST-orcl@DESKTOP-V430TU3 create global temporary table tmp(id int);
Table created.
TEST-orcl@DESKTOP-V430TU3 insert into tmp select rownum from dba_objects;
133456 rows created.
TEST-orcl@DESKTOP-V430TU3 insert into tmp select * from tmp;
133455 rows created.
TEST-orcl@DESKTOP-V430TU3 /
266910 rows created.
TEST-orcl@DESKTOP-V430TU3 /
533820 rows created.
TEST-orcl@DESKTOP-V430TU3 /
1067640 rows created.
TEST-orcl@DESKTOP-V430TU3 insert into tbl1 select * from tmp;
2135296 rows created.
TEST-orcl@DESKTOP-V430TU3 commit;
Commit complete.
TEST-orcl@DESKTOP-V430TU3 exec dbms_stats.gather_table_stats(TEST , TBL1 ,cascade= true);
PL/SQL procedure successfully completed.
TEST-orcl@DESKTOP-V430TU3 select index_name,index_type,blevel,leaf_blocks,num_rows,status,distinct_keys from user_indexes where table_name= TBL1
INDEX_NAME INDEX_TYPE BLEVEL
------------------------------ --------------------------- ----------
LEAF_BLOCKS NUM_ROWS STATUS DISTINCT_KEYS
----------- ---------- -------- -------------
IDX_TBL1_ID NORMAL 2
4662 2103843 VALID 134688
TEST-orcl@DESKTOP-V430TU3 insert into tbl1 values(null);
1 row created.
TEST-orcl@DESKTOP-V430TU3 commit;
Commit complete.
TEST-orcl@DESKTOP-V430TU3
TEST-orcl@DESKTOP-V430TU3 exec dbms_stats.gather_table_stats(TEST , TBL1 ,cascade= true);
PL/SQL procedure successfully completed.
TEST-orcl@DESKTOP-V430TU3 select index_name,index_type,blevel,leaf_blocks,num_rows,status,distinct_keys from user_indexes where table_name= TBL1
INDEX_NAME INDEX_TYPE BLEVEL
------------------------------ --------------------------- ----------
LEAF_BLOCKS NUM_ROWS STATUS DISTINCT_KEYS
----------- ---------- -------- -------------
IDX_TBL1_ID NORMAL 2
4771 2152683 VALID 134688执行查询
TEST-orcl@DESKTOP-V430TU3 set autotrace on explain
TEST-orcl@DESKTOP-V430TU3 select * from tbl1 where id is null;
ID
----------
Execution Plan
----------------------------------------------------------
Plan hash value: 312383637
--------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
--------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | 1 | 5 | 898 (2)| 00:00:11 |
|* 1 | TABLE ACCESS FULL| TBL1 | 1 | 5 | 898 (2)| 00:00:11 |
--------------------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
1 - filter(ID IS NULL)
TEST-orcl@DESKTOP-V430TU3PostgreSQL
数据表 tbl1 结构与 Oracle 一致.
testdb=# insert into tbl1 select generate_series(1,100000);
INSERT 0 100000
testdb=# explain (analyze,verbose) select * from tbl1 where id is null;
QUERY PLAN
--------------------------------------------------------------------------------------------------------
Seq Scan on public.tbl1 (cost=0.00..1569.33 rows=11 width=4) (actual time=26.052..130.752 rows=1 loops=1)
Output: id
Filter: (tbl1.id IS NULL)
Rows Removed by Filter: 110000
Planning Time: 1.403 ms
Execution Time: 130.814 ms
(6 rows)
testdb=# create index idx_tb1_id on tbl1(id);
CREATE INDEX
testdb=# explain (analyze,verbose) select * from tbl1 where id is null;
QUERY PLAN
--------------------------------------------------------------------------------------------------------
Index Only Scan using idx_tb1_id on public.tbl1 (cost=0.42..8.56 rows=4 width=4) (actual time=0.133..0.136 rows=1 loops=1)
Output: id
Index Cond: (tbl1.id IS NULL)
Heap Fetches: 1
Planning Time: 1.512 ms
Execution Time: 0.199 ms
(6 rows)使用 id is null 进行查询, 使用的是 Index Only Scan.
感谢各位的阅读，以上就是“Oracle 与 PostgreSQL 的 NULL 和索引使用区别是什么”的内容了，经过本文的学习后，相信大家对 Oracle 与 PostgreSQL 的 NULL 和索引使用区别是什么这一问题有了更深刻的体会，具体使用情况还需要大家实践验证。这里是丸趣 TV，丸趣 TV 小编将为大家推送更多相关知识点的文章，欢迎关注！
正文完
