Prepare 4 interview - Recent questions and answers in Oracle Interview Questions and Answers

Answered: How To Insert Multiple Rows with One INSERT Statement?

Sat, 02 Oct 2010 08:35:10 +0000

If you want to insert multiple rows with a single INSERT statement, you can use a subquery instead of the VALUES clause. Rows returned from the subquery will be inserted the target table.

The following tutorial exercise gives a good example:

INSERT INTO temp_links
  SELECT department_id, department_name||'.com', NULL, NULL,
    SYSDATE FROM departments WHERE department_id >= 250;
3 row created.

SELECT * FROM temp_links;
   ID URL                      NOTES     COUNTS CREATED
----- ------------------------ -------- ------- ---------
  101 dev.tempsite.com NULL           0 30-Apr-06
  102 dba.tempsite.com NULL           0 07-MAY-06
  103 sqa.tempsite.com NULL     NULL    07-MAY-06
  250 Retail Sales.com         NULL     NULL    07-MAY-06
  260 Recruiting.com           NULL     NULL    07-MAY-06
  270 Payroll.com              NULL     NULL    07-MAY-06

Answered: How To Delete All Rows a Table?

Sat, 02 Oct 2010 08:34:02 +0000

If you want to delete all rows from a table, you have two options:

Use the DELETE statement with no WHERE clause.
Use the TRUNCATE TABLE statement.
The TRUNCATE statement is more efficient the DELETE statement. The tutorial exercise shows you a good example of TRUNCATE statement:

SELECT COUNT(*) FROM temp_links;
  COUNT(*)
----------
         3

TRUNCATE TABLE temp_links;
Table truncated.

SELECT COUNT(*) FROM temp_links;
  COUNT(*)
----------
         0

How To Delete Multiple Rows from a Table?

Sat, 02 Oct 2010 08:33:55 +0000

Answered: How To Delete an Existing Row from a Table?

Sat, 02 Oct 2010 08:33:46 +0000

If you want to delete an existing row from a table, you can use the DELETE statement with a WHERE clause to identify that row. Here is good sample of DELETE statements:

INSERT INTO temp_links (url, id)
  VALUES ('newsite.com', 301);
1 row created.

SELECT * FROM temp_links WHERE id = 301;
   ID URL                      NOTES     COUNTS CREATED
----- ------------------------ -------- ------- ---------
  301 newsite.com    NULL     NULL   07-MAY-06

DELETE FROM temp_links WHERE id = 301;
1 row deleted.

SELECT * FROM temp_links WHERE id = 301;
no rows selected

What Happens If the UPDATE Subquery Returns Multiple Rows?

Sat, 02 Oct 2010 08:33:40 +0000

Answered: How To Use Values from Other Tables in UPDATE Statements?

Sat, 02 Oct 2010 08:33:33 +0000

If you want to update values in one with values from another table, you can use a subquery in the SET clause. The subquery should return only one row for each row in the update table that matches the WHERE clause. The tutorial exercise below shows a good example:

UPDATE temp_links SET (notes, created) =
  (SELECT last_name, hire_date FROM employees
    WHERE employee_id = id)
  WHERE id < 110;
3 rows updated.

SELECT * FROM temp_links WHERE id < 110;
  ID URL                      NOTES      COUNTS CREATED
---- ------------------------ --------- ------- ---------
101 dev.tempsite.com Kochhar       999 21-SEP-89
102 dba.tempsite.com De Haan         0 13-JAN-93
103 sqa.tempsite.com Hunold    NULL    03-JAN-90

This statement updated 3 rows with values from the employees table.

Answered: How To Use Existing Values in UPDATE Statements?

Sat, 02 Oct 2010 08:33:26 +0000

If a row matches the WHERE clause in a UPDATE statement, existing values in this row can be used in expressions to provide new values in the SET clause. Existing values are represented by columns in the expressions. The tutorial exercise below shows a good example:

UPDATE temp_links SET id = 1000 + id, counts = id*2
  WHERE id >= 250;
3 rows updated.

SELECT * FROM temp_links WHERE id >= 250;
   ID URL                  NOTES         COUNTS CREATED
----- -------------------- ------------ ------- ---------
1250 Retail Sales.com     Wrong URL        500 07-MAY-06
1260 Recruiting.com       Wrong URL        520 07-MAY-06
1270 Payroll.com          Wrong URL        540 07-MAY-06

This statement increased values in the id column by 1000.

How To Update Values on Multiple Rows?

Sat, 02 Oct 2010 08:33:20 +0000

Answered: How To Update Values in a Table?

Sat, 02 Oct 2010 08:33:16 +0000

If you want to update some values in one row or multiple rows in a table, you can use the UPDATE statement. The script below shows a good example:

UPDATE temp_links SET counts = 999, notes = 'Good site.'
  WHERE id = 101;
1 row updated.

SELECT * FROM temp_links WHERE id = 101;
  ID URL                      NOTES      COUNTS CREATED
---- ------------------------ ---------- ------ ---------
101 dev.tempsite.com Good site.    999 07-MAY-06

Answered: How To Omit Columns with Default Values in INSERT Statement?

Sat, 02 Oct 2010 08:32:44 +0000

If you don't want to specify values for columns that have default values, or you want to specify values to columns in an order different than how they are defined, you can provide a column list in the INSERT statement. If a column is omitted in the column, Oracle applies 3 rules:

If default value is defined for the column, that default value will be used.
If no default value is defined for the column and NULL is allowed, NULL will be used.
If no default value is defined for the column and NULL is not allowed, error will be returned.
The following tutorial exercise gives a good example:

INSERT INTO temp_links (url, id)
  VALUES ('sqa.tempsite.com', 103);
1 row created.

SELECT * FROM temp_links;
   ID URL                      NOTES     COUNTS CREATED
----- ------------------------ -------- ------- ---------
  101 dev.tempsite.com NULL           0 30-Apr-06
  102 dba.tempsite.com NULL           0 07-MAY-06
  103 sqa.tempsite.com NULL     NULL    07-MAY-06

Answered: How To Specify Default Values in INSERT Statement?

Sat, 02 Oct 2010 08:32:39 +0000

If a column is defined with a default value in a table, you can use the key word DEFAULT in the INSERT statement to take the default value for that column. The following tutorial exercise gives a good example:

INSERT INTO temp_links VALUES (102,
  'dba.tempsite.com',
  NULL,
  0,
  DEFAULT);
1 row created.

SELECT * FROM temp_links;
   ID URL                      NOTES     COUNTS CREATED
----- ------------------------ -------- ------- ---------
  101 dev.tempsite.com NULL           0 30-Apr-06
  102 dba.tempsite.com NULL           0 07-MAY-06

How To Insert a New Row into a Table?

Sat, 02 Oct 2010 08:32:33 +0000

Answered: How To Set Up SQL*Plus Output Format?

Sat, 02 Oct 2010 08:32:24 +0000

If you want to practice SQL statements with SQL*Plus, you need to set up your SQL*Plus output formatting parameter properly. The following SQL*Plus commands shows you some examples:

COLUMN id FORMAT 9999;
COLUMN url FORMAT A24;
COLUMN notes FORMAT A12;
COLUMN counts FORMAT 999999;
SET NULL 'NULL';

Answered: How To Create a Testing Table?

Sat, 02 Oct 2010 08:32:18 +0000

If you want to practice DML statements, you should create a testing table as shown in the script below:

CREATE TABLE temp_links (id NUMBER(4) PRIMARY KEY,
  url VARCHAR2(80) NOT NULL,
  notes VARCHAR2(1024),
  counts NUMBER,
  created DATE DEFAULT (sysdate));
Table created.

You should keep this table for to practice other tutorial exercises presented in this collection.

Answered: What Are DML Statements?

Sat, 02 Oct 2010 08:32:13 +0000

DML (Data Manipulation Language) statements are statements to change data values in database tables. The are 3 primary DML statements:

INSERT - Inserting new rows into database tables.
UPDATE - Updating existing rows in database tables .
DELETE - Deleting existing rows from database tables.

How To Drop an Existing View?

Sat, 02 Oct 2010 08:03:34 +0000

How To Create a New View?

Sat, 02 Oct 2010 08:03:24 +0000

How To Drop an Index?

Sat, 02 Oct 2010 08:03:18 +0000

Answered: How To Rename an Index?

Sat, 02 Oct 2010 08:03:10 +0000

Let's say you have an existing index, and you don't like its name anymore for some reason, you can rename it with the ALTER INDEX ... RENAME TO statement. Here is an example script on how to rename an index:

CREATE TABLE student (id NUMBER(5) PRIMARY KEY,
  first_name VARCHAR(80) NOT NULL,
  last_name VARCHAR(80) NOT NULL,
  birth_date DATE NOT NULL,
  social_number VARCHAR(80) UNIQUE NOT NULL);
Table created.

SELECT index_name, table_name, uniqueness
  FROM USER_INDEXES WHERE table_name = 'STUDENT';
INDEX_NAME              TABLE_NAME            UNIQUENES
----------------------- --------------------- ---------
SYS_C004153             STUDENT               UNIQUE
SYS_C004154             STUDENT               UNIQUE

ALTER INDEX SYS_C004153 RENAME TO student_pk;
Statement processed.

SELECT index_name, table_name, uniqueness
  FROM USER_INDEXES WHERE table_name = 'STUDENT';
INDEX_NAME              TABLE_NAME            UNIQUENES
----------------------- --------------------- ---------
STUDENT_PK              STUDENT               UNIQUE
SYS_C004154             STUDENT               UNIQUE

How To Create a Table Index?

Sat, 02 Oct 2010 08:03:02 +0000

How To Drop an Existing Table?

Sat, 02 Oct 2010 08:02:55 +0000

Answered: How To Delete a Column in an Existing Table?

Sat, 02 Oct 2010 08:02:48 +0000

If you have an existing column in a table and you need that column any more, you can delete it with ALTER TABLE ... DROP COLUMN statement. Here is an example SQL script:

SQL> CREATE TABLE emp_dept_90
  2 AS SELECT * FROM employees WHERE department_id=90;
Table created.

SQL> SELECT last_name FROM emp_dept_90;
LAST_NAME
-------------------------
Lname1
Lname2
Lname3

SQL> ALTER TABLE emp_dept_90 DROP COLUMN last_name;
Table altered.

SQL> SELECT last_name FROM emp_dept_90;
ERROR at line 1:
ORA-00904: "LAST_NAME": invalid identifier

As you can see the column "last_name" is gone.

Answered: How To Add a New Column to an Existing Table?

Sat, 02 Oct 2010 08:02:41 +0000

If you have an existing table with existing data rows, and want to add a new column to that table, you can use the ALTER TABLE ... ADD statement to do this. Here is an example script:

SQL> connect HR/MyCompany
Connected.

SQL> CREATE TABLE emp_dept_110
  2 AS SELECT * FROM employees WHERE department_id=110;
Table created.

SQL> ALTER TABLE emp_dept_110 ADD (vacation NUMBER);
Table altered.

SQL> SELECT first_name, last_name, vacation
  2 FROM emp_dept_110;
FIRST_NAME           LAST_NAME                   VACATION
-------------------- ------------------------- ----------
FName1              LName1
FName2              LName2

This SQL script added a new column called "vacation" to the "emp_dept_110" table. NULL values were added to this column on all existing data rows.

Answered: How To Create a New Table by Selecting Rows from Another Table?

Sat, 02 Oct 2010 08:02:33 +0000

Let's say you have a table with many data rows, now you want to create a backup copy of this table of all rows or a subset of them, you can use the CREATE TABLE...AS SELECT statement to do this. Here is an example script:

>.\\bin\\sqlplus /nolog

SQL> connect HR/MyCompany
Connected.

SQL> CREATE TABLE emp_dept_10
  2 AS SELECT * FROM employees WHERE department_id=10;
Table created.

SQL> SELECT first_name, last_name, salary
  2 FROM emp_dept_10;
FIRST_NAME           LAST_NAME                     SALARY
-------------------- ------------------------- ----------
FName1             LName1                          4400

As you can see, this SQL scripts created a table called "emp_dept_10" using the same column definitions as the "employees" table and copied data rows of one department.

This is really a quick and easy way to create a table.

How To Create a New Table?

Sat, 02 Oct 2010 08:02:22 +0000

Answered: What Are DDL Statements?

Sat, 02 Oct 2010 08:01:26 +0000

DDL (Data Definition Language) statements are statements to create and manage data objects in the database. The are 3 primary DDL statements:

CREATE - Creating a new database object.
ALTER - Altering the definition of an existing data object.
DROP - Dropping an existing data object.

Answered: How To Concatenate Two Text Values?

Sat, 02 Oct 2010 07:56:31 +0000

There are two ways to concatenate two text values together:

CONCAT() function.
'||' operation.
Here is some examples on how to use them:

SELECT 'Hell' || 'o w' || 'orld' FROM DUAL;
Hello world

SELECT CONCAT('Hello', 'world') FROM DUAL;
Hello world

Answered: What Is NULL?

Sat, 02 Oct 2010 07:55:30 +0000

NULL is a special value representing "no value" in all data types. NULL can be used on in operations like other values. But most operations has special rules when NULL is involved. The tutorial exercise below shows you some examples:

SET NULL 'NULL'; -- Make sure NULL is displayed

SELECT NULL FROM DUAL;
N
-
N
U
L
L

SELECT NULL + NULL FROM DUAL;
NULL+NULL
----------
NULL

SELECT NULL + 7 FROM DUAL;
    NULL+7
----------
NULL

SELECT NULL * 7 FROM DUAL;
    NULL*7
----------
NULL

SELECT NULL || 'A' FROM DUAL;
N
-
A

SELECT NULL + SYSDATE FROM DUAL;
NULL+SYSD
---------
NULL

How To Use Regular Expression in Pattern Match Conditions?

Fri, 01 Oct 2010 09:41:56 +0000

Answered: How To Use LIKE Conditions?

Fri, 01 Oct 2010 09:41:51 +0000

LIKE condition is also called pattern patch. There 3 main rules on using LIKE condition:

'_' is used in the pattern to match any one character.
'%' is used in the pattern to match any zero or more characters.
ESCAPE clause is used to provide the escape character in the pattern.
The following script provides you some good pattern matching examples:

SELECT CASE WHEN 'Hello world' LIKE '%world%'
  THEN 'TRUE' ELSE 'FALSE' END FROM DUAL;
TRUE

SELECT CASE WHEN 'Hello world' LIKE '%world%'
  THEN 'TRUE' ELSE 'FALSE' END FROM DUAL;
  -- Case sensitive by default
FALSE

SELECT CASE WHEN 'Hello world' LIKE '%wo_ld'
  THEN 'TRUE' ELSE 'FALSE' END FROM DUAL;
TRUE

SELECT CASE WHEN '100% correct' LIKE '100\% %' ESCAPE '\'
  THEN 'TRUE' ELSE 'FALSE' END FROM DUAL;
TRUE

How To Use IN Conditions?

Fri, 01 Oct 2010 09:41:32 +0000

How To Calculate Date and Time Differences?

Fri, 01 Oct 2010 09:41:23 +0000

How To Increment Dates by 1?

Fri, 01 Oct 2010 09:41:16 +0000

Answered: How To Use NULL as Conditions?

Fri, 01 Oct 2010 09:40:53 +0000

If you want to compare values against NULL as conditions, you should use the "IS NULL" or "IS NOT NULL" operator. Do not use "=" or "<>" against NULL. The sample script below shows you some good examples:

SELECT 'A' IS NULL FROM DUAL;
  -- Error: Boolean is not data type.
  -- Boolean can only be used as conditions

SELECT CASE WHEN 'A' IS NULL THEN 'TRUE' ELSE 'FALSE' END
  FROM DUAL;
FALSE

SELECT CASE WHEN '' IS NULL THEN 'TRUE' ELSE 'FALSE' END
  FROM DUAL;
TRUE

SELECT CASE WHEN 0 IS NULL THEN 'TRUE' ELSE 'FALSE' END
  FROM DUAL;
FALSE

SELECT CASE WHEN NULL IS NULL THEN 'TRUE' ELSE 'FALSE' END
  FROM DUAL;
TRUE

SELECT CASE WHEN 'A' = NULL THEN 'TRUE' ELSE 'FALSE' END
  FROM DUAL;
  -- Do not use "="
FALSE

SELECT CASE WHEN 'A' <> NULL THEN 'TRUE' ELSE 'FALSE' END
  FROM DUAL;
  -- Do not use "<>"
FALSE

SELECT CASE WHEN NULL = NULL THEN 'TRUE' ELSE 'FALSE' END
  FROM DUAL;
  -- Do not use "="
FALSE

Answered: How To Convert Characters to Times?

Fri, 01 Oct 2010 09:40:14 +0000

You can convert dates to characters using the TO_CHAR() function as shown in the following examples:

SELECT TO_CHAR(TO_DATE('04:49:49', 'HH:MI:SS'),
  'DD-MON-YYYY HH24:MI:SS') FROM DUAL;
  -- Default date is the first day of the current month
01-MAY-2006 04:49:49

SELECT TO_CHAR(TO_TIMESTAMP('16:52:57.847000000',
  'HH24:MI:SS.FF9'), 'DD-MON-YYYY HH24:MI:SS.FF9')
  FROM DUAL;
01-MAY-2006 16:52:57.847000000

SELECT TO_CHAR(TO_DATE('69520', 'SSSSS'),
  'DD-MON-YYYY HH24:MI:SS') FROM DUAL;
01-MAY-2006 19:18:40

How To Convert Times to Characters?

Fri, 01 Oct 2010 09:40:06 +0000

Answered: How To Convert Characters to Dates?

Fri, 01 Oct 2010 09:40:00 +0000

You can convert dates to characters using the TO_DATE() function as shown in the following examples:

SELECT TO_DATE('07-MAY-2006', 'DD-MON-YYYY') FROM DUAL;
07-MAY-06

SELECT TO_DATE('2006/05/07 ', 'YYYY/MM/DD') FROM DUAL;
07-MAY-06

SELECT TO_DATE('MAY       07, 2006', 'MONTH DD, YYYY')
  FROM DUAL;
07-MAY-06

SELECT TO_DATE('May 7, 2006', 'fmMONTH DD, YYYY') FROM DUAL;
07-MAY-06

SELECT TO_DATE('SUNDAY, MAY 7, 2006',
  'fmDAY, MONTH DD, YYYY') FROM DUAL;
07-MAY-06

How To Convert Dates to Characters?

Fri, 01 Oct 2010 09:39:55 +0000

How To Convert Characters to Numbers?

Fri, 01 Oct 2010 09:39:47 +0000

Answered: How To Convert Numbers to Characters?

Fri, 01 Oct 2010 09:39:39 +0000

You can convert numeric values to characters by using the TO_CHAR() function as shown in the following examples:

SELECT TO_CHAR(4123.4570) FROM DUAL
123.457

SELECT TO_CHAR(4123.457, '$9,999,999.99') FROM DUAL
$4,123.46

SELECT TO_CHAR(-4123.457, '9999999.99EEEE') FROM DUAL
-4.12E+03

Answered: How To Write Date and Time Interval Literals?

Fri, 01 Oct 2010 09:39:31 +0000

Date and time interval literals can coded as shown in the following samples:

SELECT DATE '2002-10-03' + INTERVAL '123-2' YEAR(3) TO MONTH
  FROM DUAL
  -- 123 years and 2 months is added to 2002-10-03
03-DEC-25

SELECT DATE '2002-10-03' + INTERVAL '123' YEAR(3) FROM DUAL
  -- 123 years is added to 2002-10-03
03-OCT-25

SELECT DATE '2002-10-03' + INTERVAL '299' MONTH(3) FROM DUAL
  -- 299 months years is added to 2002-10-03
03-SEP-27

SELECT TIMESTAMP '1997-01-31 09:26:50.124'
  + INTERVAL '4 5:12:10.222' DAY TO SECOND(3) FROM DUAL
04-FEB-97 02.39.00.346000000 PM

SELECT TIMESTAMP '1997-01-31 09:26:50.124'
  + INTERVAL '4 5:12' DAY TO MINUTE FROM DUAL
04-FEB-97 02.38.50.124000000 PM

SELECT TIMESTAMP '1997-01-31 09:26:50.124'
  + INTERVAL '400 5' DAY(3) TO HOUR FROM DUAL
07-MAR-98 02.26.50.124000000 PM

SELECT TIMESTAMP '1997-01-31 09:26:50.124'
  + INTERVAL '400' DAY(3) FROM DUAL
07-MAR-98 09.26.50.124000000 AM

SELECT TIMESTAMP '1997-01-31 09:26:50.124'
  + INTERVAL '11:12:10.2222222' HOUR TO SECOND(7) FROM DUAL
31-JAN-97 08.39.00.346222200 PM

SELECT TIMESTAMP '1997-01-31 09:26:50.124'
  + INTERVAL '30.12345' SECOND(2,4) FROM DUAL
31-JAN-97 09.27.20.247500000 AM

How To Write Date and Time Literals?

Fri, 01 Oct 2010 09:39:23 +0000

How To Write Numeric Literals?

Fri, 01 Oct 2010 09:39:16 +0000

Answered: How To Write Text Literals?

Fri, 01 Oct 2010 09:39:10 +0000

There are several ways to write text literals as shown in the following samples:

SELECT 'Hello World' FROM DUAL -- The most common format
Hello World

SELECT 'It''s Sunday!' FROM DUAL -- Single quote escaped
It's Sunday!

SELECT N'Allo, C''est moi.' FROM DUAL -- National chars
Allo, C'est moi.

SELECT Q'/It's Sunday!/' FROM DUAL -- Your own delimiter
It's Sunday!

What Are the ANSI Data Types Supported in Oracle?

Fri, 01 Oct 2010 09:39:01 +0000

Answered: What Are the Differences between BLOB and CLOB?

Fri, 01 Oct 2010 09:38:54 +0000

The main differences between BLOB and CLOB are:

BLOB stores values as LOB (Large OBject) in bitstreams.
CLOB stores values as LOB (Large OBject) in character steams.

Answered: What Are the Differences between INTERVAL YEAR TO MONTH and INTERVAL DAY TO SECOND?

Fri, 01 Oct 2010 09:38:48 +0000

The main differences between INTERVAL YEAR TO MONTH and INTERVAL DAY TO SECOND are:

INTERVAL YEAR TO MONTH stores values as time intervals at the month level.
INTERVAL DAY TO SECOND stores values as time intervals at the fractional seconds level.

What Are the Differences between DATE and TIMESTAMP?

Fri, 01 Oct 2010 09:38:40 +0000

What Are the Differences between NUMBER and BINARY_FLOAT?

Fri, 01 Oct 2010 09:38:34 +0000

Answered: What Are the Differences between CHAR and VARCHAR2?

Fri, 01 Oct 2010 09:38:25 +0000

The main differences between CHAR and VARCHAR2 are:

CHAR stores values in fixed lengths. Values are padded with space characters to match the specified length.
VARCHAR2 stores values in variable lengths. Values are not padded with any characters.