Mysql 所需的工作量与行数成正比）。你可以检查执行计划，看看它是否在使用索引。我是数据库新手，不知道这意味着什么-你可以检查执行计划，看看它是否在使用索引。你能告诉我在哪里读到的吗？ select count(rowid) from MySchema.TableI

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所需的工作量与行数成正比）。你可以检查执行计划，看看它是否在使用索引。我是数据库新手，不知道这意味着什么-你可以检查执行计划，看看它是否在使用索引。你能告诉我在哪里读到的吗？

select count(rowid) from MySchema.TableInMySchema;

create table foo (id integer not null, c1 varchar(2000), c2 varchar(2000));
insert into foo (id, c1, c2)
select lvl, c1, c1 from 
(
  select level as lvl, dbms_random.string('A', 2000) as c1
  from dual 
  connect by level < 10000
);

SQL> set autotrace traceonly explain statistics; SQL> select count(*) from foo; Execution Plan ---------------------------------------------------------- Plan hash value: 1342139204 ------------------------------------------------------------------- | Id | Operation | Name | Rows | Cost (%CPU)| Time | ------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 2740 (1)| 00:00:33 | | 1 | SORT AGGREGATE | | 1 | | | | 2 | TABLE ACCESS FULL| FOO | 9999 | 2740 (1)| 00:00:33 | ------------------------------------------------------------------- Statistics ---------------------------------------------------------- 181 recursive calls 0 db block gets 10130 consistent gets 0 physical reads 0 redo size 430 bytes sent via SQL*Net to client 420 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 5 sorts (memory) 0 sorts (disk) 1 rows processed SQL> SQL> create index i1 on foo (id); Index created. SQL> select count(*) from foo; Execution Plan ---------------------------------------------------------- Plan hash value: 129980005 ---------------------------------------------------------------------- | Id | Operation | Name | Rows | Cost (%CPU)| Time | ---------------------------------------------------------------------- | 0 | SELECT STATEMENT | | 1 | 7 (0)| 00:00:01 | | 1 | SORT AGGREGATE | | 1 | | | | 2 | INDEX FAST FULL SCAN| I1 | 9999 | 7 (0)| 00:00:01 | ---------------------------------------------------------------------- Statistics ---------------------------------------------------------- 1 recursive calls 0 db block gets 27 consistent gets 21 physical reads 0 redo size 430 bytes sent via SQL*Net to client 420 bytes received via SQL*Net from client 2 SQL*Net roundtrips to/from client 0 sorts (memory) 0 sorts (disk) 1 rows processed SQL>