DBMS 面试题与答案

If we want relational system in conjunction with time we use sixth normal form. At this moment

SQL Server does not supports it directly.

DML stands for Data Manipulation Statements. They update data values in table. Below are the most important DDL statements:- 

=>SELECT - gets data from a database table 

=> UPDATE - updates data in a table 

=> DELETE - deletes data from a database table 

=> INSERT INTO - inserts new data into a database table

DDL stands for Data definition Language. They change structure of the database objects like table, index etc. Most important DDL statements are as shown below:- 

=>CREATE TABLE - creates a new table in the database. 

=>ALTER TABLE � changes table structure in database. 

=>DROP TABLE - deletes a table from database 

=> CREATE INDEX - creates an index 

=> DROP INDEX - deletes an index

DISTINCT keyword is used to return only distinct values. Below is syntax:- Column age and

Table wbEmp

SELECT DISTINCT age FROM wbEmp

LIKE operator is used to match patterns. A "%" sign is used to define the pattern.

Below SQL statement will return all words with letter "S"

SELECT * FROM pcdsEmployee WHERE EmpName LIKE 'S%'

Below SQL statement will return all words which end with letter "S"

SELECT * FROM pcdsEmployee WHERE EmpName LIKE '%S'

Below SQL statement will return all words having letter "S" in between

SELECT * FROM pcdsEmployee WHERE EmpName LIKE '%S%'

"_" operator (we can read as �Underscore Operator�). �_� operator is the character defined at that point. In the below sample fired a query Select name from pcdsEmployee where name like

'_s%' So all name where second letter is �s� is returned.

Insert statement is used to insert new rows in to table. Update to update existing data in the

table. Delete statement to delete a record from the table. Below code snippet for Insert, Update and Delete :-

INSERT INTO wbEmployee SET name='maxwell',age='22';

UPDATE wbEmployee SET age='22' where name='maxwell';

DELETE FROM wbEmployee WHERE name = 'david';