Oracle basics

• create a table

sql> create table table_name (column datatype,column datatype]....)
sql> tablespace tablespace_name [pctfree integer] [pctused integer]
sql> [initrans integer] [maxtrans integer]
sql> storage(initial 200k next 200k pctincrease 0 maxextents 50)
sql> [logging|nologging] [cache|nocache]


• copy an existing table

sql> create table table_name [logging|nologging] as subquery


• create temporary table

sql> create global temporary table abc_temp as select * from abc
sql>on commit preserve rows/on commit delete rows


• pctfree = (average row size - initial row size) *100 /average row size


• pctused = 100-pctfree- (average row size*100/available data space)



• change storage and block utilization parameter

sql> alter table table_name pctfree=30 pctused=50 storage(next 500k
sql> minextents 2 maxextents 100);


• manually allocating extents

sql> alter table table_name allocate extent(size 500k datafile '/oracle/data.dbf');


• move tablespace

sql> alter table employee move tablespace users;


• deallocate of unused space

sql> alter table table_name deallocate unused [keep integer]


• truncate a table

sql> truncate table table_name;


• drop a table

sql> drop table table_name [cascade constraints];


• drop a column

sql> alter table table_name drop column comments cascade constraints checkpoint 1000;

alter table table_name drop columns continue;


• mark a column as unused

sql> alter table table_name set unused column comments cascade constraints;
alter table table_name drop unused columns checkpoint 1000;
alter table orders drop columns continue checkpoint 1000
data_dictionary : dba_unused_col_tabs