oracle

INDEXES

To see a table's indexes, the two important tables are user_indexes and user_ind_columns.  

CONSTRAINTS

To see a table's constraints, use these two tables:

USER_CONSTRAINTS
USER_CONS_COLUMNS

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;

PERFORMANCE

To see how a query gets implemented do set autotrace on.

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.  

PRIMARY KEYS

To create a multi-column primary key, do this:

CREATE TABLE t (
    a   NUMBER,
    b   NUMBER,
    c   VARCHAR2(100),
    PRIMARY KEY (a, b)
);

SQLPLUS VARIABLES

These can get really annoying if you're trying to run a file of SQL statements that have ampersands. These settings may be useful to you:

•

set scan {on|off}: Turns variable substitution on/off.

•

set define X: Changes the variable indicator from & to X.

•

set escape X: Changes the escape character to X. If you put this before a &, SQLPLUS doesn't treat it as a variable.

•

define varname = value: Use the define command to set &-style variables. Don't type the "&." For example:

define foo = bar

SQLPLUS WITHOUT TNSNAMES

To connect to a remote Oracle database using sqlplus without tnsnames.ora, do this:

sqlplus `username/password@(description=(address_list=(address=(protocol=tcp)(host=hostname)(port=1521)))(connect_data=(sid=sid)))'  

TRUNC

When used for dates, the syntax of TRUNC is TRUNC(date [, format]). No format is the same as `dd'. These formats are available:

•

cc,scc: century (truncates to 1 Jan.)

•

syear,syyy,y,yy,yyy,yyyy: year

•

q: quarter

•

month,mon,mm: month

•

ww: week (Truncates to Monday of the current week for any day up to 11:59:59 pm on Sunday.)

•

w: week (Truncates to X of the current week, where X is the weekday of the first day of the month.)

•

day,dy,d: week (Truncates to Sunday of the current week for any day up to 11:59:59 pm on Saturday.)

•

ddd,dd,j: day (default)

•

hh,hh12,hh24: hour

•

mi: minute

AUTHORS

Index

INDEXES

CONSTRAINTS

PERFORMANCE

PRIMARY KEYS

SQLPLUS VARIABLES

SQLPLUS WITHOUT TNSNAMES

TRUNC

AUTHORS