ORA-00900, ORA-00911 solution

SQL
DECLARE
   sql_text   VARCHAR (1000);
BEGIN
   sql_text := 'exec P_COMPILE_INVALID_OBJECTS()';

   DBMS_OUTPUT.PUT_LINE (sql_text);

   EXECUTE IMMEDIATE sql_text;
END;

Error
ORA-00900: invalid SQL statement
ORA-06512: at line 8

Solution
Use 'CALL' instead of 'EXEC' keyword.

DECLARE
   sql_text   VARCHAR (100);
BEGIN
   sql_text := 'call P_COMPILE_INVALID_OBJECTS()';

   DBMS_OUTPUT.PUT_LINE (sql_text);

   EXECUTE IMMEDIATE sql_text;
END;

SQL
DECLARE
   sql_text   VARCHAR (1000);
BEGIN
   sql_text := 'select sysdate from dual;';

   DBMS_OUTPUT.PUT_LINE (sql_text);

   EXECUTE IMMEDIATE sql_text;
END;

Error
ORA-00911: invalid character
ORA-06512: at line 8

Solution
Do not put comma (;) at the end of the sql statement.

DECLARE
   sql_text   VARCHAR (100);
BEGIN
   sql_text := 'select sysdate from dual';

   DBMS_OUTPUT.PUT_LINE (sql_text);

   EXECUTE IMMEDIATE sql_text;
END;

How to show line number in SQL Developer?

Tools -> Preferences -> Code Editor -> Line Gutter -> Activate "Show Line Numbers" -> OK

How to export/set ORACLE_SID?

Linux
export variable
$ export ORACLE_SID=XE

check variable
$ echo $ORACLE_SID

Windows
set variable
> set ORACLE_SID=XE

check variable
> echo %ORACLE_SID%

ORA-01950 Solution

Action
SQL> CREATE TABLE HR2.EMPLOYEES_NEW AS SELECT * FROM HR.EMPLOYEES;

Error
ORA-01950: no privileges on tablespace 'USERS'

Solution I
SQL> ALTER USER HR2 QUOTA 1024M ON USERS:

Solution II
SQL> GRANT UNLIMITED TABLESPACE TO HR2;

ORA-02266 solution

Action
A table has a PK (Primary Key)
B table has a FK (Foreign Key) and referenced to A table's PK

-> User tries to truncate table A

Error
ORA-02266: unique/primary keys in table referenced by enabled foreign keys

Solution I
Disable B table's FK
SQL> alter table HR.B disable constraint FK_B;
-- e.g. schema HR

Solution II
First truncate table B
SQL> truncate table B;

Then truncate table A
SQL> truncate table A;

How to disable/enable all triggers for tables?

Disable triggers for a table
SQL> alter table HR.TRG_EMPLOYEES disable all triggers;

Enable triggers for a table
SQL> alter table HR.TRG_EMPLOYEES enable all triggers;

Disable triggers belong to a schema (e.g. HR)
SQL>
DECLARE
   STR_EXEC   VARCHAR2 (1000);
BEGIN
   FOR cur_node IN (SELECT owner, table_name
                      FROM all_triggers
                     WHERE owner = 'HR')
   LOOP
      BEGIN
         str_exec :=
               'alter table '
            || cur_node.owner
            || '.'
            || cur_node.table_name
            || ' DISABLE ALL TRIGGERS';
         DBMS_OUTPUT.put_line (str_exec);

         EXECUTE IMMEDIATE str_exec;
      END;
   END LOOP;
END;
/

Enable triggers belong to a schema (e.g. HR)
SQL>
DECLARE
   STR_EXEC   VARCHAR2 (1000);
BEGIN
   FOR cur_node IN (SELECT owner, table_name
                      FROM all_triggers
                     WHERE owner = 'HR')
   LOOP
      BEGIN
         str_exec :=
               'alter table '
            || cur_node.owner
            || '.'
            || cur_node.table_name
            || ' ENABLE ALL TRIGGERS';
         DBMS_OUTPUT.put_line (str_exec);

         EXECUTE IMMEDIATE str_exec;
      END;
   END LOOP;
END;
/

ORA-01045 solution

Error
ORA-01045: user HR lacks CREATE SESSION privilege; logon denied

Solution
Grant CREATE SESSION privilege to 'HR' user
SQL> grant CREATE SESSION to HR;

ORA-28000 solution

Error
ORA-28000: the account is locked

Solution
Find the assigned profile for related user
SQL> select profile from DBA_USERS where username = 'HR';
-- e.g. DEFAULT

Disable failed_login_attempts parameter
SQL> alter profile "DEFAULT" limit failed_login_attempts UNLIMITED;

Check it
SQL> select resource_name,limit from dba_profiles where profile='DEFAULT';

Apply the new setting for user
SQL> alter user "HR" ACCOUNT UNLOCK;

How to enable/disable DBA auto task jobs?

Jobs
Automatic Optimizer Statistics Collection -> Gathers stale or missing statistics
Automatic Segment Advisor -> Identifies segments that reorganized to save space
Automatic SQL Tuning Advisor -> Tune high load SQL

Check auto tasks
SQL> SELECT client_name, status FROM dba_autotask_client;

To disable all auto task jobs
SQL> EXEC DBMS_AUTO_TASK_ADMIN.disable;

To enable all auto task jobs
SQL> EXEC DBMS_AUTO_TASK_ADMIN.enable;

To disable a spesific task
SQL> EXEC DBMS_AUTO_TASK_ADMIN.DISABLE(client_name=>'sql tuning advisor', operation=>NULL, window_name=>NULL);

SQL> EXEC DBMS_AUTO_TASK_ADMIN.DISABLE(client_name=>'auto space advisor', operation=>NULL, window_name=>NULL);

SQL> EXEC DBMS_AUTO_TASK_ADMIN.DISABLE(client_name=>'auto optimizer stats collection', operation=>NULL, window_name=>NULL);

To enable a spesific task
SQL> EXEC DBMS_AUTO_TASK_ADMIN.ENABLE(client_name=>'sql tuning advisor', operation=>NULL, window_name=>NULL);

SQL> EXEC DBMS_AUTO_TASK_ADMIN.ENABLE(client_name=>'auto space advisor', operation=>NULL, window_name=>NULL);

SQL> EXEC DBMS_AUTO_TASK_ADMIN.ENABLE(client_name=>'auto optimizer stats collection', operation=>NULL, window_name=>NULL);

Ref: https://smarttechways.com/2015/09/03/disable-and-enable-auto-task-job-for-11g-and-12c-version-in-oracle/

e.g. shrink table usage

Steps:
SQL>
exec dbms_stats.gather_table_stats('HR','EMPLOYEES');
-- Gathering table statistics

SQL>
SELECT owner,
       table_name,
       ROUND ( (num_rows * avg_row_len) / (1024 * 1024)) MB
  FROM dba_tables
 WHERE table_name = 'EMPLOYEES';
-- Check table actual size

SQL>
  SELECT table_name,
         ROUND ( (blocks * 8) / 1024, 2) "size (MB)",
         ROUND ( (num_rows * avg_row_len / 1024 / 1024), 2) "actual_data (MB)",
         (  ROUND ( (blocks * 8) / 1024, 2)
          - ROUND ( (num_rows * avg_row_len / 1024 / 1024), 2))
            "wasted_space (MB)"
    FROM dba_tables
   WHERE     (ROUND ( (blocks * 8), 2) >
                 ROUND ( (num_rows * avg_row_len / 1024), 2))
         AND table_name = 'EMPLOYEES'
         AND OWNER LIKE 'HR'
ORDER BY 4 DESC;
-- Check table current, actual, wasted size

SQL>
ALTER TABLE HR.EMPLOYEES ENABLE ROW MOVEMENT;
-- Enable feature before the operation

SQL>
ALTER TABLE HR.EMPLOYEES SHRINK SPACE COMPACT;
-- Online operation without HWM (High Water Mark) fix

SQL>
ALTER TABLE HR.EMPLOYEES SHRINK SPACE;
-- Table will be locked for any DML commands 

SQL>
ALTER TABLE HR.EMPLOYEES DISABLE ROW MOVEMENT;
-- Disable feature after the operation

SQL>
  SELECT table_name,
         ROUND ( (blocks * 8) / 1024, 2) "size (MB)",
         ROUND ( (num_rows * avg_row_len / 1024 / 1024), 2) "actual_data (MB)",
         (  ROUND ( (blocks * 8) / 1024, 2)
          - ROUND ( (num_rows * avg_row_len / 1024 / 1024), 2))
            "wasted_space (MB)"
    FROM dba_tables
   WHERE     (ROUND ( (blocks * 8), 2) >
                 ROUND ( (num_rows * avg_row_len / 1024), 2))
         AND table_name = 'EMPLOYEES'
         AND OWNER LIKE 'HR'
ORDER BY 4 DESC;
-- Lastly, Check table current, actual, wasted size again

Ref: http://select-star-from.blogspot.com.tr/2013/09/how-to-check-table-fragmentation-in.html

DBMS_JOBS vs DBMS_SCHEDULER

-> DBMS_SCHEDULER introduced in 10g releases so before this, we were able to use only DBMS_JOBS for scheduler jobs.

e.g. DBMS_JOBS
SQL>
VARIABLE job_id NUMBER;
BEGIN
  DBMS_JOB.submit (
    job       => :job_id,
    what      => 'BEGIN P_KILL_ALL_INACTIVE_SESSIONS; END;',
    next_date => SYSDATE,
    interval  => 'SYSDATE + 1 /* 1 Day */');
  COMMIT;
END;
/
PRINT job_id

e.g. DBMS_SCHEDULER
SQL>
BEGIN
  DBMS_SCHEDULER.create_job (
    job_name        => 'example_job',
    job_type        => 'PLSQL_BLOCK',
    job_action      => 'BEGIN P_KILL_ALL_INACTIVE_SESSIONS; END;',
    start_date      => SYSTIMESTAMP,
    repeat_interval => 'SYSTIMESTAMP + 1 /* 1 Day */');
END;
/

Ref for example: https://ozsoyler.blogspot.com.tr/2017/02/how-to-kill-all-inactive-sessions-with.html

How to monitor TEMP tablespace resource usage?

-> Check Total TEMP usage:
SQL>
SELECT B.TOTAL_MB,
       B.TOTAL_MB - ROUND (A.USED_BLOCKS * 8 / 1024) CURRENT_FREE_MB,
       ROUND (USED_BLOCKS * 8 / 1024) CURRENT_USED_MB,
       ROUND (MAX_USED_BLOCKS * 8 / 1024) MAX_USED_MB
  FROM V$SORT_SEGMENT A,
       (SELECT ROUND (SUM (BYTES) / 1024 / 1024) TOTAL_MB FROM DBA_TEMP_FILES) B;

-> Check Total TEMP usage according to database blocks:
SQL>
SELECT DISTINCT S.SID,
                  S.USERNAME,
                  U.TABLESPACE,
                  S.SQL_HASH_VALUE || '/' || U.SQLHASH HASH_VALUE,
                  U.SEGTYPE,
                  U.CONTENTS,
                  U.BLOCKS
    FROM V$SESSION S, V$TEMPSEG_USAGE U
   WHERE S.SADDR = U.SESSION_ADDR
ORDER BY U.BLOCKS DESC;

-> Find problematic SQL for TEMP
SQL>
SELECT 
      S.SID
     ,S.CLIENT_INFO
     ,S.MACHINE
     ,S.PROGRAM
     ,S.TYPE
     ,S.LOGON_TIME
     ,S.OSUSER
     ,SQ.SORTS
     ,SQ.DISK_READS
     ,SQ.BUFFER_GETS
     ,SQ.ROWS_PROCESSED
     ,SQ.SQLTYPE
     ,SQ.SQL_TEXT
 FROM GV$SESSION S    
    , GV$SQL SQ
WHERE S.SQL_HASH_VALUE = SQ.HASH_VALUE
  --AND s.inst_id= 1
  AND S.SID = 555 
  AND SQ.INST_ID= S.INST_ID;

e.g. simple DDL audit trigger

e.g. DDL audit trigger

CREATE TABLE SYSTEM.audit_ddl_history
(
osuser varchar2(50),
session_user varchar2(50),
host varchar2(50),
terminal varchar2(50),
object_owner varchar2(50),
obejct_type varchar2(50),
object_name varchar2(50),
sysevent varchar2(50),
audit_date date
);

CREATE OR REPLACE TRIGGER SYSTEM.ALPERDB_AUDIT_HISTORY
   AFTER DDL
   ON DATABASE
begin
if (ora_sysevent='GRANT')
  then
  NULL; -- don't care to grant!
  else
    insert into SYSTEM.audit_ddl_history(osuser, session_user, host, terminal, object_owner, obejct_type, object_name, sysevent,audit_date)
    values(
      sys_context('USERENV','OS_USER') ,
      sys_context('USERENV','SESSION_USER') , 
      sys_context('USERENV','HOST') , 
      sys_context('USERENV','TERMINAL') ,
      ora_dict_obj_owner,
      ora_dict_obj_type,
      ora_dict_obj_name,
      ora_sysevent,
    sysdate
    );
  end if;
end;
/

e.g.
SQL>
SELECT SYS_CONTEXT ('USERENV', 'SESSION_USER') FROM DUAL;

Ref: https://docs.oracle.com/cd/B10501_01/appdev.920/a96590/adg14evt.htm

Solution ORA-01031, ORA-01994

Error
ORA-01031: insufficient privileges

Solution
Give sysdba role to sys
SQL> grant sysdba to sys; 

If you get this error ->
ORA-01994: GRANT failed: password file missing or disabled

Run following command;
$ orapwd file=$ORACLE_HOME/dbs/orapw$ORACLE_SID password=alper entries=2 force=y
-> entries; number of users can login as sysdba role
-> force; enable to overwrite current pwd file

Check remote_login parameter
SQL> show parameter remote_login_passwordfile;

If remote_login_passwordfile is not "EXCLUSIVE";
Change it permanently:
add this into init.ora file;
*.remote_login_passwordfile='EXCLUSIVE'

Check who has sysdba role in database lastly
SQL> select * from V$PWFILE_USERS;

How to start/stop/configure samba service?

If you need, uninstall old samba
# yum erase samba samba-common samba-client 

install tool
# yum install samba4

or upgrade tool
# yum upgrade samba4

configure settings
# vi /etc/samba/smb.conf

e.g.
[share_folder]
 comment = Share Folder
 path = /share_folder
 create mode = 0777
 readonly = no
 browseable = yes
 public = yes

Check configuration of samba
# testparm

check samba service and version
# smbstatus

startup options
# chkconfig smb on
# service smb start

connect to share folder
e.g. 
RUN> \\10.10.10.10\share_folder

remove startup option and stop vnc
# chkconfig smb off
# service smb stop

ORA-28002 solution

Error
ORA-28002: the password will expire within [A] days

Solution
Disable password expiration
SQL> select profile from DBA_USERS where username = 'HR';
-- e.g. DEFAULT

Change password_life_time parameter
SQL> alter profile "DEFAULT" limit password_life_time UNLIMITED;

Check it
SQL> select resource_name,limit from dba_profiles where profile='DEFAULT';

Apply the new setting for user
SQL> alter user "HR" identified by "hr";

SQL PLUS system parameters usage (set/show)

To show parameter in detail
SQL> SHOW DEFINE;

To escape from substitution variable (&):
SQL> SET DEFINE OFF;

To enable DBMS_OUTPUT:
SQL> SET SERVEROUTPUT ON;

To see old and new values of variables:
SQL> SET VERIFY ON;

To calculate total execution time of SQL:
SQL> SET TIMING ON;

To print time on the SQL terminal:
SQL> SET TIME ON;

To see table columns name and types for a table:
SQL> DESC hr.employees@XE;

To see currently logged-in user:
SQL> SHOW user;

e.g. changing the DBID and Database Name

e.g.
Backup database
RMAN> backup database

Mount database
SQL> shu immediate;
SQL> startup mount;

Change DBID
$ nid TARGET=SYS

or

Change both DBID and DBNAME
$ nid TARGET=SYS DBNAME=new_xe

Change database name from parameter file (init.ora)
*.db_name='NEW_XE'

Mount database again
SQL> startup mount;

Open database
SQL> alter database open resetlogs;

Ref: https://docs.oracle.com/database/121/SUTIL/GUID-05B4733C-9EAA-438F-A2A4-4E84EB1E1E65.htm#SUTIL1544s

SYS_CONTEXT function parameters and examples

Active parameters
ACTION, AUDITED_CURSORID, AUTHENTICATED_IDENTITY, AUTHENTICATION_DATA, AUTHENTICATION_METHOD, BG_JOB_ID, CLIENT_IDENTIFIER, CLIENT_INFO, CURRENT_BIND, CURRENT_SCHEMA, CURRENT_SCHEMAID, CURRENT_SQL, CURRENT_SQLn, CURRENT_SQL_LENGTH, DB_DOMAIN, DB_NAME, DB_UNIQUE_NAME, ENTRYID, ENTERPRISE_IDENTITY, FG_JOB_ID, GLOBAL_CONTEXT_MEMORY, GLOBAL_UID, HOST, IDENTIFICATION_TYPE, INSTANCE, INSTANCE_NAME, IP_ADDRESS, ISDBA, LANG, LANGUAGE, MODULE, NETWORK_PROTOCOL, NLS_CALENDAR, NLS_CURRENCY, NLS_DATE_FORMAT, NLS_DATE_LANGUAGE, NLS_SORT, NLS_TERRITORY, OS_USER, POLICY_INVOKER, PROXY_ENTERPRISE_IDENTITY, PROXY_GLOBAL_UID, PROXY_USER, SERVER_HOST, SERVICE_NAME, SESSION_USER, SESSION_USERID,  SESSIONID, SID, STATEMENTID, TERMINAL

e.g.
SQL> select SYS_CONTEXT ('USERENV', 'SESSION_USER') from dual;
-- HR
e.g.
SQL> select SYS_CONTEXT ('USERENV', 'CURRENT_SCHEMA') from dual;
-- HR

Deprecated parameters
AUTHENTICATION_TYPE, CURRENT_USER, CURRENT_USERID, EXTERNAL_NAME

Extra for sys_context
Link

Ref: http://docs.oracle.com/cd/B19306_01/server.102/b14200/functions165.htm

Quiesce restricted mode vs Restricted mode

Differences;
* Quiesce restricted option is less raugh than restricted option and they are quite similar.
* In quiesce restricted option, active session allows to continue until it become inactive.
* In restricted session, only new users can login who has "restrict session" privileges, but in quiesce restricted session, system blocks new non-dba users.

commands;
SQL> ALTER SYSTEM QUIESCE RESTRICTED;

check the state;
SQL> SELECT ACTIVE_STATE FROM V$INSTANCE;
-- normal, quiescing, quiesced

SQL> ALTER SYSTEM UNQUIESCE;

check the state;
SQL> SELECT ACTIVE_STATE FROM V$INSTANCE;
-- normal, quiescing, quiesced

SQL> ALTER SYSTEM ENABLE RESTRICTED SESSION;

SQL> ALTER SYSTEM DISABLE RESTRICTED SESSION;

Ref: https://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:902149038276