These are the possible values for user_cons_columns.constraint_type:
P = Primary Key C = Check (e.g. NOT NULL) R = Reference (foreign key) U = Unique V = "with check option" (for views)
If you are looking at Reference-style constraints, TABLE_NAME and COLUMN_NAME in the constraint-related data dictionary tables refer to the dependent table--that is, the table with the foreign key, not the table with the primary key. For instance, suppose you have a product table whose primary key is product_code, and suppose cart_item.product_code is a reference to it. Then the constraint tables will show CART_ITEM as the table_name and PRODUCT_CODE as the column_name. To see where the reference points, you must use user_constraints.r_constraint_name. That holds the name of the primary key constraint on the referenced table.
Therefore, if you want to see which tables depend on product.product_code, use this query:
SELECT ucc.constraint_name, ucc.table_name, ucc.column_name FROM user_constraints uc1, user_constraints uc2, user_cons_columns ucc WHERE uc1.table_name = 'PRODUCT' AND uc1.constraint_type = 'P' AND uc2.r_constraint_name = uc1.constraint_name AND ucc.constraint_name = uc2.constraint_name ORDER BY ucc.position;
Here's a great query to get performance information. It returns all the queries that have run since Oracle started, ordered by buffer_gets.
SELECT executions, ROUND(executions / extot * 100, 3) as expct, disk_reads, round(disk_reads / executions, 3) as drperexec, round(disk_reads / drtot * 100, 3) as drpct, buffer_gets, round(buffer_gets / executions, 3) as bgperexec, round(buffer_gets / bgtot * 100, 3) as bgpct, rows_processed, sorts, runtime_mem, parsing_user_id, sql_text FROM v$sqlarea, (SELECT sum(executions) as extot, sum(disk_reads) as drtot, sum(buffer_gets) as bgtot, sum(rows_processed) as rptot, sum(sorts) as sorttot FROM v$sqlarea) WHERE disk_reads > 10000 and buffer_gets > 10000 ORDER BY buffer_gets;
To limit the query to a single user, add 'WHERE parsing_user_id = ...', where the id is a number from dba_users, not the username.
CREATE TABLE t ( a NUMBER, b NUMBER, c VARCHAR2(100), PRIMARY KEY (a, b) );
define foo = bar