Oracle Architecture Overview

Oracle terms Schema – logical collection of user’s objects Tablespace – logical space used for storage Datafile – physical file used for storage Extent – group of contiguous blocks Block – unit of physical storage

System Global Area (SGA) Oracle Architecture database vs. instance Database Instance Parameter files* Control files** Data files Redo Log files System Global Area (SGA) Background Processes Memory Disk * Parameter files include the init<SID>.ora and config<SID>.ora files. These are used to set options for the database. ** Control files contain information about the db in binary form. They can be backed up to a text file however.

Oracle vs. Access and MySQL One .mdb file contains all objects Limited roles/permissions MySQL Three files per table Permissions based on user, database, and host Oracle Many files Many roles/permissions possible

The Oracle Data Dictionary Collection of tables and views that show the inner workings and structure of the db “static” data dictionary views owned by SYS created by catalog.sql script at db creation contain DDL info dynamic data dictionary views also referred to as V$ views based on virtual tables (X$ tables) provide info about the instance

More Data Dictionary 1. Samples table created in user’s schema Create table samples ( ID number(3) primary key, Type varchar2(5), Constraint type_ck check (type in (‘photo’,’swatch’)) …); 1. Samples table created in user’s schema 2. Primary key index created in user’s schema (SYS_C984620) 3. Data dictionary is also updated, with rows being inserted into tables underlying the following data dictionary views: User_objects User_constraints User_cons_columns And lots more…

Oracle Odds and Ends Dual table % - the SQL wildcard inserting apostrophes Case sensitive string matching SELECT 1+1*400 FROM DUAL; SELECT ename FROM emp WHERE ename like ‘%neil%’; INSERT INTO emp (name) VALUES (‘O’’Neill); UPDATE emp SET ename=UPPER(ename) WHERE ename='O''Neill';

Sysdate ADATE Sysdate returns current system date AND time use trunc function to remove time piece Example: select to_char (adate, ‘dd-mon-yy hh24:mi:ss’) TO_CHAR(ADATE, ‘DD-MON-YY:HH24:MI:SS’) 17-feb-00 23:41:50 select adate from samples where trunc(adate)=‘17-feb-00’; ADATE 17-FEB-00

ROWID ROWID is an internal number Oracle uses to uniquely identify each row NOT a primary key! Is the actual location of a row on a disk. Very efficient for retrieval. Format specifies block, row, and file (and object in 8) Oracle 7: BBBBBBB.RRRR.FFFFF Oracle 8: OOOOOO.FFF.BBBBBB.RRR Called pseudo-column since can be selected

Outer joins in Oracle Add (+) to table where nulls are acceptable SELECT * FROM emp, dept WHERE emp.deptno(+)=dept.id;

Oracle SQL functions Upper(), lower() Substr(), replace(), rtrim(), concat() Length() Floor(), sqrt(), min(), max(), stddev() Add_months(), months_between(), last_day() To_date(), to_char(), to_lob()

More functions nvl() decode() If NULL, return this instead… Nvl(lastname,’Anonymous’) decode() Sort of like an If/Then statement… Decode(gender,0,’Male’,1,’Female’,’Unknown’)

Oracle error messages Divided into groups by first three letters (e.g. ORA or TNS) Number gives more information about error Several messages may be related to only one problem oerr facility

Constraints Primary key Foreign key Unique, not null Check Name your constraints User_constraints, user_cons_columns CREATE TABLE test ( id NUMBER(2), col2 VARCHAR2(2), col3 VARCHAR2(3), CONSTRAINT test_pk PRIMARY KEY(id), CONSTRAINT col3_ck CHECK (col3 IN ('yes','no')) );

NAME T SEARCH_CONDITION --------------- - ------------------------- SELECT user_constraints.constraint_name name, constraint_type type, user_constraints.search_condition FROM user_constraints, user_cons_columns WHERE user_constraints.table_name=user_cons_columns.table_name AND user_constraints.constraint_name=user_cons_columns.constraint_name AND user_constraints.owner=user_cons_columns.owner AND user_constraints.table_name=‘TEST’; NAME T SEARCH_CONDITION --------------- - ------------------------- COL3_CK C col3 IN ('yes','no') TEST_PK P

Constraints Oracle naming of constraints is NOT intuitive! enabling and disabling disable constraint constraint_name; the EXCEPTIONS table run utlexcpt.sql to create EXCEPTIONS table then alter SQL statement: SQL_query EXCEPTIONS into EXCEPTIONS; What constraints do *YOU* have in your schema? @h:\..\chaffin\shared\scripts\utlexcpt.sql

More objects Sequences Synonyms creating the sequence create sequence CustomerID increment by 1 start with 1000; selecting from the sequence insert into customer (name, contact, ID) values (‘TManage’,’Kristin Chaffin’,CustomerID.NextVal); CurrVal is used after NextVal for related inserts Synonyms provide location and owner transparency Can be public or private

PL/SQL - Triggers Executed on insert, update, delete Use to enforce business logic that can’t be coded through referential integrity or constraints Types of triggers row level (use FOR EACH ROW clause) statement level (default) Before and After triggers Referencing old and new values

Trigger example SQL> desc all_triggers; Name Null? Type ------------------------------- -------- ---- OWNER VARCHAR2(30) TRIGGER_NAME VARCHAR2(30) TRIGGER_TYPE VARCHAR2(16) TRIGGERING_EVENT VARCHAR2(75) TABLE_OWNER VARCHAR2(30) BASE_OBJECT_TYPE VARCHAR2(16) TABLE_NAME VARCHAR2(30) COLUMN_NAME VARCHAR2(4000) REFERENCING_NAMES VARCHAR2(128) WHEN_CLAUSE VARCHAR2(4000) STATUS VARCHAR2(8) DESCRIPTION VARCHAR2(4000) ACTION_TYPE VARCHAR2(11) TRIGGER_BODY LONG

Trigger example (cont.) SQL> select trigger_name from all_triggers where owner='SCOTT'; TRIGGER_NAME ------------------------------ AFTER_INS_UPD_ON_EMP set lines 120 col trigger_name format a20 col triggering_event format a18 col table_name format a10 col description format a26 col trigger_body format a35 select trigger_name, trigger_type, triggering_event, table_name, status, description, trigger_body from all_triggers where trigger_name='AFTER_INS_UPD_ON_EMP';

Trigger example (cont.) SQL> / TRIGGER_NAME TRIGGER_TYPE TRIGGERING_EVENT TABLE_NAME STATUS DESCRIPTION -------------------- ---------------- ------------------ ---------- -------- ----------------------- TRIGGER_BODY ----------------------------------- AFTER_INS_UPD_ON_EMP BEFORE EACH ROW INSERT OR UPDATE EMP ENABLED scott.after_ins_upd_on_emp before insert or update on scott.emp for each row begin :new.ename := upper(:new.ename); end; The above trigger was created with the following statement: create or replace trigger scott.after_ins_upd_on_emp before insert or update on scott.emp for each row begin :new.ename := upper(:new.ename); end;

Remember those views? Query USER_TRIGGERS to get trigger info Query USER_SOURCE to get source of procedure, function, package, or package body Query USER_ERRORS to get error information (or use show errors) col name format a15 col text format a40 select name, type, text from user_errors order by name, type, sequence; Query USER_OBJECT to get status info

Understanding Indexes Index overhead impact on inserts, updates and deletes batch inserts can be slowed by indexes - may want to drop, then recreate rebuilding indexes Use indexes when query will return less than 5% of rows in a large table Determining what to index All primary and foreign keys Examine SQL and index heavily hit, selective columns (columns often found in where clauses)

What not to Index…preferably columns that are constantly updated columns that contain a lot of null values columns that have a poor distribution of data Examples: yes/no true/false male/female

B*-tree index Branch blocks Leaf blocks Miller Deal – ROWID < Davis Davis Jones Smith Turner Turner > Adams Brown Culver Deal Howard Isis Jules Klein Main Moss Porter Sikes Sykes Thomas Topper Vera Wagner Yanks 1+ levels of branch blocks – these contain info about range of values contained in next level. Only 1 level of leaf blocks – contain actual index values and rowids for associated rows “Depth” of index refers to the number of branch levels between the root and leaf blocks. Reverse key index reverses the values before storing them (e.g. value of ‘ABCD’ would be stored as ‘DCBA’) – this tends to address the problem of standard b*tree indexes where they become unbalanced over time (and thus less efficient and deeper, requiring more depth on the right side than the left side due to growth and deletion of values over time). Function-based indexes can be either b*tree or bitmap and are simply based on the results of a function, rather than on the value of a row. Leaf blocks Deal – ROWID Howard – ROWID Isis - ROWID Detail of leaf node Figure 4-1. in Oracle Essentials (2001). Greenwald, et.al. O’Reilly. p 92

Bitmap index Parts table Bitmapped index on ‘color’ partno color size 1 2 3 4 GREEN RED RED BLUE MED MED SMALL LARGE Bitmapped index on ‘color’ color = ‘BLUE’ color = ‘RED’ color = ‘GREEN’ 0 0 0 1 0 1 1 0 1 0 0 0 Part number 1 2 3 4 Figure 4-2. in Oracle Essentials (2001). Greenwald, et.al. O’Reilly. p 95