CSC Asked Oracle SQL Queries In Written Test Interview

CSC Frequently Asked Oracle SQL Queries In Written Test Interview Questions

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;

Computer Sciences Corporation Frequently Asked Oracle SQL Queries In Written Test Interview Questions

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 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;

Write a SQL query to find the products which does not have sales at all?

Solution:

“LG” is the only product which does not have sales at all. This can be achieved in three ways.

Method 1: Using left outer join.

SELECT P.PRODUCT_NAME
FROM   PRODUCTS P
       LEFT OUTER JOIN
       SALES S
ON     (P.PRODUCT_ID = S.PRODUCT_ID);
WHERE  S.QUANTITY IS NULL

PRODUCT_NAME
------------
LG

Method 2: Using the NOT IN operator.

SELECT P.PRODUCT_NAME
FROM   PRODUCTS P
WHERE  P.PRODUCT_ID NOT IN
       (SELECT DISTINCT PRODUCT_ID FROM SALES);

PRODUCT_NAME
------------
LG

Method 3: Using the NOT EXISTS operator.

SELECT P.PRODUCT_NAME
FROM   PRODUCTS P
WHERE  NOT EXISTS
       (SELECT 1 FROM SALES S WHERE S.PRODUCT_ID = P.PRODUCT_ID);

PRODUCT_NAME
------------
LG

Write a SQL query to find the products whose sales decreased in 2012 compared to 2011?

Solution:

Here Nokia is the only product whose sales decreased in year 2012 when compared with the sales in the year 2011. The SQL query to get the required output is

SELECT P.PRODUCT_NAME
FROM   PRODUCTS P,
       SALES S_2012,
       SALES S_2011
WHERE  P.PRODUCT_ID = S_2012.PRODUCT_ID
AND    S_2012.YEAR = 2012
AND    S_2011.YEAR = 2011
AND    S_2012.PRODUCT_ID = S_2011.PRODUCT_ID
AND    S_2012.QUANTITY < S_2011.QUANTITY;

PRODUCT_NAME
------------
Nokia

Write a query to select the top product sold in each year?

Solution:

Nokia is the top product sold in the year 2010. Similarly, Samsung in 2011 and IPhone, Samsung in 2012. The query for this is

SELECT PRODUCT_NAME,
       YEAR
FROM
(
SELECT P.PRODUCT_NAME,
       S.YEAR,
       RANK() OVER (
              PARTITION BY S.YEAR
              ORDER BY S.QUANTITY DESC
              ) RNK
FROM   PRODUCTS P,
       SALES S
WHERE  P.PRODUCT_ID = S.PRODUCT_ID
) A
WHERE RNK = 1;