Re: What does this mean ? DDL

"mark" <mark_brehmen_at_yahoo.com> wrote in message news:fa4781e4.0110232323.4cc6a539_at_posting.google.com...
> Hello all
>
> This is a view description of ALL_TABLES i got from TOAD(see end). It
> would be helpful if someone could tell me about the bitand functions.
> some stuff i read about this bit operators is going over my head :-(.
>
> I have seen Thomas Kytes functions to convert from Base 2 to Hex and
> such. It really beats me how it can be useful when we talk about a
> database. I mean why would anyone want to concern themselves with
> hexadecimals in a database. Or for that matter try to convert from
> decimal system to base 2? Can anyone give an example?
>
> I did not study computer science. So if someone could help with this i
> will be grateful.
>
>
> CREATE OR REPLACE VIEW ALL_TABLES ( OWNER,
> TABLE_NAME, TABLESPACE_NAME, CLUSTER_NAME, IOT_NAME,
> PCT_FREE, PCT_USED, INI_TRANS, MAX_TRANS,
> INITIAL_EXTENT, NEXT_EXTENT, MIN_EXTENTS, MAX_EXTENTS,
> PCT_INCREASE, FREELISTS, FREELIST_GROUPS, LOGGING,
> BACKED_UP, NUM_ROWS, BLOCKS, EMPTY_BLOCKS,
> AVG_SPACE, CHAIN_CNT, AVG_ROW_LEN, AVG_SPACE_FREELIST_BLOCKS,
> NUM_FREELIST_BLOCKS, DEGREE, INSTANCES, CACHE,
> TABLE_LOCK, SAMPLE_SIZE, LAST_ANALYZED, PARTITIONED,
> IOT_TYPE, TEMPORARY, NESTED, BUFFER_POOL
> ) AS select u.name, o.name,decode(bitand(t.property, 32), 32, null,
> decode(bitand(t.property, 64), 64, null, ts.name)),
> decode(bitand(t.property, 1024), 0, null, co.name),
> decode(bitand(t.property, 512), 0, null, co.name),
> decode(bitand(t.property, 32), 0, mod(t.pctfree$, 100), null),
> decode(bitand(t.property, 32), 0, t.pctused$, null),
> decode(bitand(t.property, 32), 0, t.initrans, null),
> decode(bitand(t.property, 32), 0, t.maxtrans, null),
> s.iniexts * ts.blocksize, s.extsize * ts.blocksize,
> s.minexts, s.maxexts, s.extpct,
> decode(s.lists, 0, 1, s.lists), decode(s.groups, 0, 1,
> s.groups),
> decode(bitand(t.property, 32), 32, null,
> decode(bitand(t.flags, 32), 0, 'YES', 'NO')),
> decode(bitand(t.flags,1), 0, 'Y', 1, 'N', '?'),
> t.rowcnt, t.blkcnt, t.empcnt, t.avgspc, t.chncnt, t.avgrln,
> t.avgspc_flb, t.flbcnt,
> lpad(decode(t.degree, 32767, 'DEFAULT', nvl(t.degree,1)),10),
> lpad(decode(t.instances, 32767, 'DEFAULT',
> nvl(t.instances,1)),10),
> lpad(decode(bitand(t.flags, 8), 8, 'Y', 'N'),5),
> decode(bitand(t.flags, 6), 0, 'ENABLED', 'DISABLED'),
> t.samplesize, t.analyzetime,
> decode(bitand(t.property, 32), 32, 'YES', 'NO'),
> decode(bitand(t.property, 64), 64, 'IOT',
> decode(bitand(t.property, 512), 512, 'IOT_OVERFLOW',
> null)),
> decode(bitand(o.flags, 2), 0, 'N', 2, 'Y', 'N'),
> decode(bitand(t.property, 8192), 8192, 'YES',
> decode(bitand(t.property, 1), 0, 'NO', 'YES')),
> decode(s.cachehint, 0, 'DEFAULT', 1, 'KEEP', 2, 'RECYCLE',
> NULL)
> from sys.user$ u, sys.ts$ ts, sys.seg$ s, sys.obj$ co, sys.tab$ t,
> sys.obj$ o
> where o.owner# = u.user#
> and o.obj# = t.obj#
> and bitand(t.property, 1) = 0
> and t.bobj# = co.obj# (+)
> and t.ts# = ts.ts#
> and t.file# = s.file# (+)
> and t.block# = s.block# (+)
> and t.ts# = s.ts# (+)
> and (o.owner# = userenv('SCHEMAID')
> or o.obj# in
> (select oa.obj#
> from sys.objauth$ oa
> where grantee# in ( select kzsrorol
> from x$kzsro
> )
> )
> or /* user has system privileges */
> exists (select null from v$enabledprivs
> where priv_number in (-45 /* LOCK ANY TABLE */,
> -47 /* SELECT ANY TABLE */,
> -48 /* INSERT ANY TABLE */,
> -49 /* UPDATE ANY TABLE */,
> -50 /* DELETE ANY TABLE */)
> )
> )

What Oracle seems to have done in the dictionary is to compress several YES/NO or boolean fields in one column.
The column functions as a mask
7 6 5 4 3 2 1 0
1 1 0 0 1 1 0 1

Apparently to know whether a table is an index organised table they need to retrieve information from bit 6 ( 2 to the power of 6 is 64) when you calculate t.property AND 64
you calculate the following

110001101
and

010000000

1 and 0 returns 0
1 and 1 returns 1
so this calculation will
return (if you apply it bit for bit 1)
0100000 so 64

So that's why they have this decode

       decode(bitand(t.property, 64), 64, 'IOT',
               decode(bitand(t.property, 512), 512, 'IOT_OVERFLOW'

which simply means
'if bit 6 of the property column is 1, this is an index organized table, otherwise test whether bit 9 is 1 (2^9 = 512),and return IOT_OVERFLOW

It is a very efficient way to store information in one single column, though admittedly very complicated.

You should leave the all_tables view at what it is, so I'm not sure what you wan t to do with it.

Hth,

Sybrand Bakker
Senior Oracle DBA Received on Wed Oct 24 2001 - 03:03:47 CDT