http://viralpatel.net/blogs/useful-oracle-queries/
Here’s a list of 40+ Useful Oracle queries that every Oracle developer must bookmark. These queries range from date manipulation, getting server info, get execution status, calculate database size etc.
Date / Time related queries
-
Get the first day of the month
Quickly returns the first day of current month. Instead of current month you want to find first day of month where a date falls, replace SYSDATE with any date column/value.
SELECT
TRUNC (SYSDATE,
‘MONTH‘
)
"First day of current month"
FROM
DUAL;
-
Get the last day of the month
This query is similar to above but returns last day of current month. One thing worth noting is that it automatically takes care of leap year. So if you have 29 days in Feb, it will return 29/2. Also similar to above query replace SYSDATE with any other date column/value to find last day of that particular month.
SELECT
TRUNC (LAST_DAY (SYSDATE))
"Last day of current month"
FROM
DUAL;
-
Get the first day of the Year
First day of year is always 1-Jan. This query can be use in stored procedure where you quickly want first day of year for some calculation.
SELECT
TRUNC (SYSDATE,
‘YEAR‘
)
"Year First Day"
FROM
DUAL;
-
Get the last day of the year
Similar to above query. Instead of first day this query returns last day of current year.
SELECT
ADD_MONTHS (TRUNC (SYSDATE,
‘YEAR‘
), 12) - 1
"Year Last Day"
FROM
DUAL
-
Get number of days in current month
Now this is useful. This query returns number of days in current month. You can change SYSDATE with any date/value to know number of days in that month.
SELECT
CAST
(TO_CHAR (LAST_DAY (SYSDATE),
‘dd‘
)
AS
INT
) number_of_days
FROM
DUAL;
-
Get number of days left in current month
Below query calculates number of days left in current month.
SELECT
SYSDATE,
LAST_DAY (SYSDATE)
"Last"
,
LAST_DAY (SYSDATE) - SYSDATE
"Days left"
FROM
DUAL;
-
Get number of days between two dates
Use this query to get difference between two dates in number of days.
SELECT
ROUND ( (MONTHS_BETWEEN (
‘01-Feb-2014‘
,
‘01-Mar-2012‘
) * 30), 0)
num_of_days
FROM
DUAL;
OR
SELECT
TRUNC(sysdate) - TRUNC(e.hire_date)
FROM
employees;
Use second query if you need to find number of days since some specific date. In this example number of days since any employee is hired.
-
Display each months start and end date upto last month of the year
This clever query displays start date and end date of each month in current year. You might want to use this for certain types of calculations.
SELECT
ADD_MONTHS (TRUNC (SYSDATE,
‘MONTH‘
), i) start_date,
TRUNC (LAST_DAY (ADD_MONTHS (SYSDATE, i))) end_date
FROM
XMLTABLE (
‘for $i in 0 to xs:int(D) return $i‘
PASSING XMLELEMENT (
d,
FLOOR (
MONTHS_BETWEEN (
ADD_MONTHS (TRUNC (SYSDATE,
‘YEAR‘
) - 1, 12),
SYSDATE)))
COLUMNS i
INTEGER
PATH
‘.‘
);
-
Get number of seconds passed since today (since 00:00 hr)
SELECT
(SYSDATE - TRUNC (SYSDATE)) * 24 * 60 * 60 num_of_sec_since_morning
FROM
DUAL;
-
Get number of seconds left today (till 23:59:59 hr)
SELECT
(TRUNC (SYSDATE+1) - SYSDATE) * 24 * 60 * 60 num_of_sec_left
FROM
DUAL;
Data dictionary queries
-
Check if a table exists in the current database schema
A simple query that can be used to check if a table exists before you create it. This way you can make your create table script rerunnable. Just replace table_name with actual table you want to check. This query will check if table exists for current user (from where the query is executed).
SELECT
table_name
FROM
user_tables
WHERE
table_name =
‘TABLE_NAME‘
;
-
Check if a column exists in a table
Simple query to check if a particular column exists in table. Useful when you tries to add new column in table using ALTER TABLE statement, you might wanna check if column already exists before adding one.
SELECT
column_name
AS
FOUND
FROM
user_tab_cols
WHERE
table_name =
‘TABLE_NAME‘
AND
column_name =
‘COLUMN_NAME‘
;
-
Showing the table structure
This query gives you the DDL statement for any table. Notice we have pass ‘TABLE’ as first parameter. This query can be generalized to get DDL statement of any database object. For example to get DDL for a view just replace first argument with ‘VIEW’ and second with your view name and so.
SELECT
DBMS_METADATA.get_ddl (
‘TABLE‘
,
‘TABLE_NAME‘
,
‘USER_NAME‘
)
FROM
DUAL;
-
Getting current schema
Yet another query to get current schema name.
SELECT
SYS_CONTEXT (
‘userenv‘
,
‘current_schema‘
)
FROM
DUAL;
-
Changing current schema
Yet another query to change the current schema. Useful when your script is expected to run under certain user but is actually executed by other user. It is always safe to set the current user to what your script expects.
ALTER
SESSION
SET
CURRENT_SCHEMA = new_schema;
Database administration queries
-
Database version information
Returns the Oracle database version.
SELECT
*
FROM
v$version;
-
Database default information
Some system default information.
SELECT
username,
profile,
default_tablespace,
temporary_tablespace
FROM
dba_users;
-
Database Character Set information
Display the character set information of database.
SELECT
*
FROM
nls_database_parameters;
-
Get Oracle version
SELECT
VALUE
FROM
v$system_parameter
WHERE
name
=
‘compatible‘
;
-
Store data case sensitive but to index it case insensitive
Now this ones tricky. Sometime you might querying database on some value independent of case. In your query you might do UPPER(..) = UPPER(..) on both sides to make it case insensitive. Now in such cases, you might want to make your index case insensitive so that they don’t occupy more space. Feel free to experiment with this one.
CREATE
TABLE
tab (col1 VARCHAR2 (10));
CREATE
INDEX
idx1
ON
tab (
UPPER
(col1));
ANALYZE
TABLE
a COMPUTE
STATISTICS
;
-
Resizing Tablespace without adding datafile
Yet another DDL query to resize table space.
ALTER
DATABASE
DATAFILE
‘/work/oradata/STARTST/STAR02D.dbf‘
resize 2000M;
-
Checking autoextend on/off for Tablespaces
Query to check if autoextend is on or off for a given tablespace.
SELECT
SUBSTR (file_name, 1, 50), AUTOEXTENSIBLE
FROM
dba_data_files;
(
OR
)
SELECT
tablespace_name, AUTOEXTENSIBLE
FROM
dba_data_files;
-
Adding datafile to a tablespace
Query to add datafile in a tablespace.
ALTER
TABLESPACE data01
ADD
DATAFILE
‘/work/oradata/STARTST/data01.dbf‘
SIZE
1000M AUTOEXTEND
OFF
;
-
Increasing datafile size
Yet another query to increase the datafile size of a given datafile.
ALTER
DATABASE
DATAFILE
‘/u01/app/Test_data_01.dbf‘
RESIZE 2G;
-
Find the Actual size of a Database
Gives the actual database size in GB.
SELECT
SUM
(bytes) / 1024 / 1024 / 1024
AS
GB
FROM
dba_data_files;
-
Find the size occupied by Data in a Database or Database usage details
Gives the size occupied by data in this database.
SELECT
SUM
(bytes) / 1024 / 1024 / 1024
AS
GB
FROM
dba_segments;
-
Find the size of the SCHEMA/USER
Give the size of user in MBs.
SELECT
SUM
(bytes / 1024 / 1024)
"size"
FROM
dba_segments
WHERE
owner =
‘&owner‘
;
-
Last SQL fired by the User on Database
This query will display last SQL query fired by each user in this database. Notice how this query display last SQL per each session.
SELECT
S.USERNAME ||
‘(‘
|| s.sid ||
‘)-‘
|| s.osuser UNAME,
s.program ||
‘-‘
|| s.terminal ||
‘(‘
|| s.machine ||
‘)‘
PROG,
s.sid ||
‘/‘
|| s.serial# sid,
s.status
"Status"
,
p.spid,
sql_text sqltext
FROM
v$sqltext_with_newlines t, V$SESSION s, v$process p
WHERE
t.address = s.sql_address
AND
p.addr = s.paddr(+)
AND
t.hash_value = s.sql_hash_value
ORDER
BY
s.sid, t.piece;
Performance related queries
-
CPU usage of the USER
Displays CPU usage for each User. Useful to understand database load by user.
SELECT
ss.username, se.SID, VALUE / 100 cpu_usage_seconds
FROM
v$session ss, v$sesstat se, v$statname sn
WHERE
se.STATISTIC# = sn.STATISTIC#
AND
NAME
LIKE
‘%CPU used by this session%‘
AND
se.SID = ss.SID
AND
ss.status =
‘ACTIVE‘
AND
ss.username
IS
NOT
NULL
ORDER
BY
VALUE
DESC
;
-
Long Query progress in database
Show the progress of long running queries.
SELECT
a.sid,
a.serial#,
b.username,
opname OPERATION,
target OBJECT,
TRUNC (elapsed_seconds, 5)
"ET (s)"
,
TO_CHAR (start_time,
‘HH24:MI:SS‘
) start_time,
ROUND ( (sofar / totalwork) * 100, 2)
"COMPLETE (%)"
FROM
v$session_longops a, v$session b
WHERE
a.sid = b.sid
AND
b.username
NOT
IN
(
‘SYS‘
,
‘SYSTEM‘
)
AND
totalwork > 0
ORDER
BY
elapsed_seconds;
-
Get current session id, process id, client process id?
This is for those who wants to do some voodoo magic using process ids and session ids.
SELECT
b.sid,
b.serial#,
a.spid processid,
b.process clientpid
FROM
v$process a, v$session b
WHERE
a.addr = b.paddr
AND
b.audsid = USERENV (
‘sessionid‘
);
- V$SESSION.SID AND V$SESSION.SERIAL# is database process id
- V$PROCESS.SPID is shadow process id on this database server
- V$SESSION.PROCESS is client PROCESS ID, ON windows it IS : separated THE FIRST # IS THE PROCESS ID ON THE client AND 2nd one IS THE THREAD id.
-
Last SQL Fired from particular Schema or Table:
SELECT
CREATED,
TIMESTAMP
, last_ddl_time
FROM
all_objects
WHERE
OWNER =
‘MYSCHEMA‘
AND
OBJECT_TYPE =
‘TABLE‘
AND
OBJECT_NAME =
‘EMPLOYEE_TABLE‘
;
-
Find Top 10 SQL by reads per execution
SELECT
*
FROM
(
SELECT
ROWNUM,
SUBSTR (a.sql_text, 1, 200) sql_text,
TRUNC (
a.disk_reads / DECODE (a.executions, 0, 1, a.executions))
reads_per_execution,
a.buffer_gets,
a.disk_reads,
a.executions,
a.sorts,
a.address
FROM
v$sqlarea a
ORDER
BY
3
DESC
)
WHERE
ROWNUM < 10;
-
Oracle SQL query over the view that shows actual Oracle connections.
SELECT
osuser,
username,
machine,
program
FROM
v$session
ORDER
BY
osuser;
-
Oracle SQL query that show the opened connections group by the program that opens the connection.
SELECT
program application,
COUNT
(program) Numero_Sesiones
FROM
v$session
GROUP
BY
program
ORDER
BY
Numero_Sesiones
DESC
;
-
Oracle SQL query that shows Oracle users connected and the sessions number for user
SELECT
username Usuario_Oracle,
COUNT
(username) Numero_Sesiones
FROM
v$session
GROUP
BY
username
ORDER
BY
Numero_Sesiones
DESC
;
-
Get number of objects per owner
SELECT
owner,
COUNT
(owner) number_of_objects
FROM
dba_objects
GROUP
BY
owner
ORDER
BY
number_of_objects
DESC
;
Utility / Math related queries
-
Convert number to words
More info: Converting number into words in Oracle
SELECT
TO_CHAR (TO_DATE (1526,
‘j‘
),
‘jsp‘
)
FROM
DUAL;
Output:
one thousand five hundred twenty-six
-
Find string in package source code
Below query will search for string ‘FOO_SOMETHING’ in all package source. This query comes handy when you want to find a particular procedure or function call from all the source code.
--search a string foo_something in package source code
SELECT
*
FROM
dba_source
WHERE
UPPER
(text)
LIKE
‘%FOO_SOMETHING%‘
AND
owner =
‘USER_NAME‘
;
-
Convert Comma Separated Values into Table
The query can come quite handy when you have comma separated data string that you need to convert into table so that you can use other SQL queries like IN or NOT IN. Here we are converting ‘AA,BB,CC,DD,EE,FF’ string to table containing AA, BB, CC etc. as each row. Once you have this table you can join it with other table to quickly do some useful stuffs.
WITH
csv
AS
(
SELECT
‘AA,BB,CC,DD,EE,FF‘
AS
csvdata
FROM
DUAL)
SELECT
REGEXP_SUBSTR (csv.csvdata,
‘[^,]+‘
, 1,
LEVEL
) pivot_char
FROM
DUAL, csv
CONNECT
BY
REGEXP_SUBSTR (csv.csvdata,
‘[^,]+‘
, 1,
LEVEL
)
IS
NOT
NULL
;
-
Find the last record from a table
This ones straight forward. Use this when your table does not have primary key or you cannot be sure if record having max primary key is the latest one.
SELECT
*
FROM
employees
WHERE
ROWID
IN
(
SELECT
MAX
(ROWID)
FROM
employees);
(
OR
)
SELECT
*
FROM
employees
MINUS
SELECT
*
FROM
employees
WHERE
ROWNUM < (
SELECT
COUNT
(*)
FROM
employees);
-
Row Data Multiplication in Oracle
This query use some tricky math functions to multiply values from each row. Read below article for more details.
More info: Row Data Multiplication In OracleWITH
tbl
AS
(
SELECT
-2 num
FROM
DUAL
UNION
SELECT
-3 num
FROM
DUAL
UNION
SELECT
-4 num
FROM
DUAL),
sign_val
AS
(
SELECT
CASE
MOD (
COUNT
(*), 2)
WHEN
0
THEN
1
ELSE
-1
END
val
FROM
tbl
WHERE
num < 0)
SELECT
EXP (
SUM
(LN (
ABS
(num)))) * val
FROM
tbl, sign_val
GROUP
BY
val;
-
Generating Random Data In Oracle
You might want to generate some random data to quickly insert in table for testing. Below query help you do that. Read this article for more details.
More info: Random Data in OracleSELECT
LEVEL
empl_id,
MOD (ROWNUM, 50000) dept_id,
TRUNC (DBMS_RANDOM.VALUE (1000, 500000), 2) salary,
DECODE (ROUND (DBMS_RANDOM.VALUE (1, 2)), 1,
‘M‘
, 2,
‘F‘
) gender,
TO_DATE (
ROUND (DBMS_RANDOM.VALUE (1, 28))
||
‘-‘
|| ROUND (DBMS_RANDOM.VALUE (1, 12))
||
‘-‘
|| ROUND (DBMS_RANDOM.VALUE (1900, 2010)),
‘DD-MM-YYYY‘
)
dob,
DBMS_RANDOM.STRING (
‘x‘
, DBMS_RANDOM.VALUE (20, 50)) address
FROM
DUAL
CONNECT
BY
LEVEL
< 10000;
-
Random number generator in Oracle
Plain old random number generator in Oracle. This ones generate a random number between 0 and 100. Change the multiplier to number that you want to set limit for.
--generate random number between 0 and 100
SELECT
ROUND (DBMS_RANDOM.VALUE () * 100) + 1
AS
random_num
FROM
DUAL;
-
Check if table contains any data
This one can be written in multiple ways. You can create count(*) on a table to know number of rows. But this query is more efficient given the fact that we are only interested in knowing if table has any data.
SELECT
1
FROM
TABLE_NAME
WHERE
ROWNUM = 1;
If you have some cool query that can make life of other Oracle developers easy, do share in comment section.