query to find keys in a table

hi

i have this query which tells what are the primary keys in a table

SELECT cols.table_name, cols.column_name, cols.position, cons.status, cons.owner
FROM all_constraints cons, all_cons_columns cols
WHERE cols.table_name = 'PERSON_DATA'
AND cons.constraint_type = 'P'
AND cons.constraint_name = cols.constraint_name
AND cons.owner = cols.owner
ORDER BY cols.table_name, cols.position;

Any one care to explain what are the tables : all_constraints and all_cons_columns
and what is cons.constraint_type = 'P'

Thanks
royjaydAsked:
Who is Participating?
 
awking00Commented:
all_constraints and all_cons_columns are system dictionay views containing metadata of the database. The all_ prefix allows you to get information on objects that you own or have access to (the dba_ prefix is for all objects and the user_prefix is only for objects you own).
The constraint_type values available are:
C - Check constraint on a table
P - Primary key
U - Unique key
R - Referential integrity
V - With check option, on a view
O - With read only, on a view
H - Hash expression
F - Constraint that involves a REF column
S - Supplemental logging

Some additional links -
http://psoug.org/reference/constraints.html
http://docs.oracle.com/cd/B28359_01/server.111/b28320/statviews_1042.htm
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slightwv (䄆 Netminder) Commented:
>>all_constraints
>>all_cons_columns
>>cons.constraint_type = 'P'

All of this is in the docs:
http://docs.oracle.com/cd/E11882_01/server.112/e25513/statviews_1046.htm

http://docs.oracle.com/cd/E11882_01/server.112/e25513/statviews_1044.htm
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royjaydAuthor Commented:
slightwv

A simple one or two liners with a layman explanation would have helped :-)
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slightwv (䄆 Netminder) Commented:
I'm not sure I could have explained it better than the docs do.
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royjaydAuthor Commented:
thanks.
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