COUNT(*)计算行数有哪些优化手段

COUNT(*)计算行数有哪些优化手段 --无索引 DROP TABLE T_20170704_COUNT_LHR_01 PURGE; CREATE TABLE T_20170704_COUNT_LHR_01 AS  SELECT * FROM DBA_OBJECTS; ALTER TABLE T_20170704_COUNT_LHR_01 MODIFY OBJECT_NAME NOT NULL;

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