Trim characters from a string in oracle

• For trimming characters from last 

select  substr('Trim_India_1', 0, length('Trim_India_1')-2) from dual;

Result: Trim_India

• For trimming characters from starting 

select  substr('Trim_India_1', 3) from dual;

Result: im_India_1

This will return all characters starting from position 3

How To Resolve Database Blocking In Oracle

Database blocking is a situation where the statement run by one user locks a record or set of records and another statement run by the same user or different user requires a conflicting lock type on the record or records, locked by the first user.

Database blocking issue is a very common scenario in any application.

How to Identify the blocking session
1. DBA_BLOCKERS  : Gives information only about the blocking session.

SQL> select * from dba_blockers;
HOLDING_SESSION
—————
252

 

2. v$LOCK  : Gives details of blocking and waiting session.

SQL> select l1.sid, ‘ IS BLOCKING ‘, l2.sid
from v$lock l1, v$lock l2
where l1.block =1 and l2.request > 0
and l1.id1=l2.id1
and l1.id2=l2.id2
/

SID ‘ISBLOCKING’         SID
———- ————- ———-
244  IS BLOCKING         252

 

To get more specific details use the below query:

 

SQL> select s1.username || ‘@’ || s1.machine
|| ‘ ( SID=’ || s1.sid || ‘ )  is blocking ‘
|| s2.username || ‘@’|| s2.machine || ‘ ( SID=’ || s2.sid || ‘ ) ‘ AS blocking_status
from v$lock l1, v$session s1, v$lock l2, v$session s2
where s1.sid=l1.sid and s2.sid=l2.sid
and l1.BLOCK=1 and l2.request > 0
and l1.id1 = l2.id1
and l2.id2 = l2.id2 ;

BLOCKING_STATUS
——————————————————————————–
MECK@machine1 ( SID=244 )  is blocking TAMY@machine2 ( SID=252 )

 

How to Identify the locked object

SQL> select * from v$lock ;

ADDR             KADDR                          SID TY        ID1        ID2             LMODE   REQUEST   CTIME     BLOCK
—————- —————-                    ———- –       ———- ———- ——-    ———-       ———- ———-
0000000451723DE8 0000000451723E20        244 TX    1310745    3139497          6          0         166           1

000000046032AFE0 000000046032B000        252 TX    1310745    3139497          0          6          33             0

 

TYPES OF LOCKS -  UL, TX amd TM
1. UL is a user-defined lock This is a lock defined with the DBMS_LOCK package.
2. TX lock is a row transaction lock; it’s acquired once for every transaction that changes data.Number of objects are being changed does not matter. The ID1 and ID2 columns point to the rollback segment and transaction table entries for that transaction.
3. TM lock is a DML lock. It’s acquired once for each object that’s being changed. The ID1 column identifies the object being modified.

So to find the object that is being blocked we can use ID1 from the v$lock.

SQL> select object_name from dba_objects where object_id=307193;

OBJECT_NAME
————–
OBJ1

How to Identify the locked row ?

SQL> select do.object_name,
row_wait_obj#, do.data_object_id, row_wait_file#, row_wait_block#, row_wait_row#,
dbms_rowid.rowid_create ( 1, do.data_object_id, ROW_WAIT_FILE#, ROW_WAIT_BLOCK#, ROW_WAIT_ROW# )
from v$session s, dba_objects do
where sid=252
and s.ROW_WAIT_OBJ# = do.OBJECT_ID ;

OBJECT_NAME
——————————————————————————–
ROW_WAIT_OBJ# DATA_OBJECT_ID ROW_WAIT_FILE# ROW_WAIT_BLOCK# ROW_WAIT_ROW#
————- ————– ————– ————— ————-
DBMS_ROWID.ROWID_C
——————
OBJ1
307193         307193              5             455             0
AABK/5AAFAAAAHHAAA

From this, we get the row directly:
SQL> select * from obj1 where rowid=’ AABK/5AAFAAAAHHAAA’ ;

Getting the sql query that is being blocked
If you got the sid it should be easy by using the following sql :
SQL>select s.sid, q.sql_text from v$sqltext q, v$session s
where q.address = s.sql_address
and s.sid = 252;

SID SQL_TEXT
—– —————————————————————-
252 update obj1 set bar=:”SYS_B_0″ where bar=:”SYS_B_1″

Finding the blocking session SID and Serial#.

SQL> Select blocking_session, sid, serial#, wait_class,seconds_in_wait From v$session where blocking_session is not NULL order by blocking_session;

BLOCKING_SESSION     SID    SERIAL#  WAIT_CLASS     SECONDS_IN_WAIT
—————- ———- ———- ————————————————–
244                             252  11049       Application        1634

Solution to resolve locking
Kill the blocking session.
SQL> alter system kill session 244,11049′ immediate;

System altered.

 

sp_whoisactive and sp_who3

For looking into some SQL performance problems on systems I normally use these procedures.

sp_whoisactive 
sp_who3 

On running sp_whoisactive, if the output is showing a CXPACKET wait type that’s when sp_who3 comes into play.  Running sp_who3 with a SPID number after the procedure like “exec sp_who3 125″ will give you the wait type for each thread within the process.

When doing this recently on a system sp_whoisactive showed me that CXPACKET was the wait type.  After digging into the process with sp_who3 I saw that one of the threads was waiting on SOS_SCHEDULER_YIELD.  I then used sp_whoisactive to get the execution plan showing me the missing index which needed to be created.  In this case there was a clustered index on the table which was being scanned.  Based on the page count output from SET STATISTICS IO we were scanning the entire table every time the query was run.  This massively expensive query was causing the query to parallelize and the run time to go insanely high.

Hopefully you’ll find these stored procedures to be useful in your performance troubleshooting.  They aren’t hard to use, but they sure are useful.

sp_who3 - A new version of sp_who2

While working I came across this interesting version of sp_who2 named as sp_who3

It can be most useful when trying to diagnose slow running queries as it can provide a wealth of information in a single screen.

CREATE PROCEDURE sp_who3 

( 
    @SessionID int = NULL
) 
AS
BEGIN
SELECT
    SPID                = er.session_id 
    ,Status             = ses.status 
    ,[Login]            = ses.login_name 
    ,Host               = ses.host_name 
    ,BlkBy              = er.blocking_session_id 
    ,DBName             = DB_Name(er.database_id) 
    ,CommandType        = er.command 
    ,SQLStatement       = 
        SUBSTRING
        ( 
            qt.text, 
            er.statement_start_offset/2, 
            (CASE WHEN er.statement_end_offset = -1 
                THEN LEN(CONVERT(nvarchar(MAX), qt.text)) * 2 
                ELSE er.statement_end_offset 
                END - er.statement_start_offset)/2 
        ) 
    ,ObjectName         = OBJECT_SCHEMA_NAME(qt.objectid,dbid) + '.' + OBJECT_NAME(qt.objectid, qt.dbid) 
    ,ElapsedMS          = er.total_elapsed_time 
    ,CPUTime            = er.cpu_time 
    ,IOReads            = er.logical_reads + er.reads 
    ,IOWrites           = er.writes 
    ,LastWaitType       = er.last_wait_type 
    ,StartTime          = er.start_time 
    ,Protocol           = con.net_transport 
    ,ConnectionWrites   = con.num_writes 
    ,ConnectionReads    = con.num_reads 
    ,ClientAddress      = con.client_net_address 
    ,Authentication     = con.auth_scheme 
FROM sys.dm_exec_requests er 
LEFT JOIN sys.dm_exec_sessions ses ON ses.session_id = er.session_id 
LEFT JOIN sys.dm_exec_connections con  ON con.session_id = ses.session_id 
OUTER APPLY sys.dm_exec_sql_text(er.sql_handle) as qt 
WHERE er.session_id > 50 
    AND @SessionID IS NULL OR er.session_id = @SessionID 
ORDER BY
    er.blocking_session_id DESC
    ,er.session_id 
  
END

Usage:
exec sp_who3

Useful SQL Developer Shortcuts

A short list of some useful shortcuts of SQL Developer.

Key	Description
Ctrl+Alt+R	Check for updated data
Ctrl+Alt+W	Toggle focus between popup and primary window
Ctrl+/	Toggles line commenting
Ctrl+Alt+0. . .Ctrl+Alt+5	Switch diagram layout
Ctrl+5	Strikethrough
Ctrl+A	Select all
Ctrl+B	Boldface
Ctrl+Alt+C	Toggle source code editing
Ctrl+E	Center alignment
Ctrl+H	Create hyperlink
Ctrl+Shift+H	Remove hyperlink
Ctrl+I	Italics
Ctrl+L	Full justified alignment
Ctrl+Shift+L	Left alignment
Ctrl+Alt+L	Numbered list
Ctrl+M	Increase indentation
Ctrl+Shift+M	Decrease indentation
Ctrl+Alt+M	Launch context menu
Ctrl+R	Right alignment
Ctrl+Alt+R	Toggle rich text editing
Ctrl+Shift+S	Clear text styles
Ctrl+U	Underline
Ctrl+Y	Redo
Ctrl+Z	Undo
Ctrl+Shift+^	Go up one level
Ctrl+N	New file will be open.
Ctrl+O	Opens the existing file.
Alt+V+C	Opens the connections window.
Alt+F10	Select connection and open new worksheet.
Ctrl+Shift+D	Duplicate the line
Ctrl+'(Single Quote)	Toggle the case (Upper/Lower/Initcap)
Ctrl+ Enter	Executes the current statement
Ctrl+ Space	Invokes code insight on demand
Ctrl-Up/Dn	Replaces worksheet with previous/next SQL from SQL History
Shift+F4	Opens a Describe window for current object at cursor
Ctrl+F7	Format SQL
Ctrl+ Space	Executes the current statement

As a developer I used Bold ones the most. They are my favorite.

Toggle case in SQL DEVELOPER

Toad users find SQL developers shortcuts bit difficult. I searched a lot and then finally find out the shortcut for CASE TOGGLE in SQL Developer as well



Ctrl+'(Single Quote)  -->   Toggle the case (Upper/Lower/Initcap)

Sample Query:     select emp_id , emp_name from employees


1) On Ctrl+'(Single Quote) query change all keywords to upper case

SELECT emp_id , emp_name FROM employees


2) On again doing Ctrl+'(Single Quote) full query changes to upper case except keywords

select EMP_ID , EMP_NAME from EMPLOYEES


3) On again doing Ctrl+'(Single Quote) full query changes to upper case except keywords

Select Emp_Id , Emp_Name From Employees


4) On again doing Ctrl+'(Single Quote) full query changes to upper case

SELECT EMP_ID , EMP_NAME FROM EMPLOYEES


5) On again doing Ctrl+'(Single Quote) full query changes to lower case

select emp_id , emp_name from employees

Useful Oracle Queries

Date / Time related queries

1. 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;

2. 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;

3. 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;

4. 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

5. 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;

6. 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;

7. 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.

8. 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 '.');

9. 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;

10. 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

11. 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';

12. 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';

13. 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;

14. Getting current schema

    Yet another query to get current schema name.
    

    SELECT SYS_CONTEXT ('userenv', 'current_schema') FROM DUAL;

15. 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

16. Database version information

    Returns the Oracle database version.
    

    SELECT * FROM v$version;

17. Database default information

    Some system default information.
    

    SELECT username,        profile,        default_tablespace,        temporary_tablespace   FROM dba_users;

18. Database Character Set information

    Display the character set information of database.
    

    SELECT * FROM nls_database_parameters;

19. Get Oracle version

    SELECT VALUE   FROM v$system_parameter  WHERE name = 'compatible';

20. 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;

21. Resizing Tablespace without adding datafile

    Yet another DDL query to resize table space.
    

    ALTER DATABASE DATAFILE '/work/oradata/STARTST/STAR02D.dbf' resize 2000M;

22. 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;

23. 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;

24. 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;

25. 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;

26. 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;

27. 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';

28. 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

29. 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;

30. 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;

31. 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.

32. 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';

33. 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;

34. Oracle SQL query over the view that shows actual Oracle connections.

    SELECT osuser,          username,          machine,          program     FROM v$session ORDER BY osuser;

35. 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;

36. 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;

37. 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

38. 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

39. 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';

40. 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;

41. 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);

42. 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 Oracle
    

    WITH 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;

43. 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 Oracle
    

    SELECT 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;

44. 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;

45. 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;