Answer / sat!sh

Compression is used to Minimize the table size, for example
when the table size is increasing anonymously We can use
Compression to reduce the size of the table

Conditions:
1.Compression can be declared at the time of table creation
2.We can compress up to 256 column values(not columns)
3.We can't compress variable length fields
(vartext,varchar..)

Explanation for 2 condition:

create table tab1
(
:
:
Order_type char(25) compress ('air','sea','road')
:
)
in the above example order type have 3 fields, one should
be selected by the user, so one of the field will repeat
for every order, like these column values we can use
compress statement because these are repeating for entire
table, like these column values TD supports 256 col

generally NCR people will provides ready made scripts for
these type of compressions

----
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Answer / veni botcha

Hey Buddy!!

U r mistaken we can only compress 255 distinct values per
column plus nulls(by default).
Compressed values are stored in table header.
also compression cannot be done on primary index columns
and alter table does not support compression on existing
columns.
Compression works with multi-set tables.

Answer / yuvaevergreen

Use of compress is multivalue compression saves space and
adds speed.

Answer / ismail

Both of ur answers about the number of columns values that
can be compressed (255 distinct values/single value) are
correct. Versions upto V2R4 allows only single value
compression. Since V2R5 multi-value compression is possible.

Answer / vinay

@Veni ...FYI Compression works with SET tables as well.

Answer / tdguy

Highly common values are used for compression. More space
can be saved. The value is stored in table header.
Datatypes like INTERVAL, TIME, TIMESTAMP, VARBYTE and
VARCHAR cannot be compressed.

Answer / yuvaevergreen

Compression helps in enhanced storage, improved response
time, CPU savings.
Select Currentperm from DBC.tablesize where
tablename='tablename'; Using the permsize, we can know about
the percentage space saved.

Answer / surendra

Now, 13.10 is equiped with 510 characters wide compression
including more datatypes. The ALC which helps to use the UDF
is adding more power to compression. I feel happy that the
MVC and ALC can work together which also reduce the further
effort while working on a compressed data column.

Answer / bkishor

We can compress VARCHAR also in TD14 Version

Answer / rahul

I heart about in Teradata 14 ,NCR allows compress on varchar columns as well ,upto 510 character please correct me if i m wrong.

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