oracle :
单索引
create index 索引名称 on table(column)
删除索引
drop index 索引名称
复合索引
create index WBSINDEX ON project_info(wbs,is_delete)
查询某张表中所有索引
select * from ALL_INDEXS where table_name = project_info
查询某张表加了索引的列
select * from ALL_IND_COLUMN where table_name = project_info
索引优缺点:
优点 : 加快查询速度
缺点 : 更新,要把索引也进行更新
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