Lab 2

SQL

Data Manipulation Language

(DML)

Eng. Ibraheem Lubbad

The Islamic University of Gaza

Faculty of Engineering

Dept. of Computer Engineering

Database Lab (ECOM 4113)

SQL stands for Structured Query Language, it’s a standard language for accessing

and manipulating databases.

SQL commands are case insensitive instructions used to communicate with the

database to perform specific tasks, work, functions and queries with data. All SQL

statements start with any of the keywords like SELECT, INSERT, UPDATE, DELETE,

ALTER, DROP, CREATE, USE, SHOW and all the statements end with a semicolon (;)

SQL commands are grouped into major categories depending on their

functionality:

Data Manipulation Language (DML) - These SQL commands are used

for storing, retrieving, modifying, and deleting data. These Data

Manipulation Language commands are CALL, DELETE, EXPLAIN,

INSERT, LOCK TABLE, MERGE, SELECT and UPDATE.

Data Definition Language (DDL) - These SQL commands are used for

creating, modifying, and dropping the structure of database objects.

The commands are ALTER, ANALYZE, AUDIT, COMMENT, CREATE, DROP,

FLASHBACK, GRANT, PURGE, RENAME, REVOKE and TRUNCATE.

Transaction Control Language (TCL) - These SQL commands are used

for managing changes affecting the data. These commands are

COMMIT, ROLLBACK, and SAVEPOINT.

Data Control Language (DCL) - These SQL commands are used for providing security to database objects. These commands are GRANT and REVOKE.

In our lab we will use university schema (you can open it by click on file)

SELECT Statement:

The SELECT statement retrieves data from a database. The data is returned in a table-like structure called a result-set. SELECT is the most frequently used action on a database. To create a simple SQL SELECT Statement, you must specify the column(s) name and the table name.

The whole query is called SQL SELECT Statement.

-table-name : is the name of the table from which the information is retrieved.

-column_list : includes one or more columns from which data is retrieved.

-The code within the brackets is optional.

Retrieve data by specific column:

Syntax of SQL Select Statement

SELECT * | {[DISTINCT] column_list | expression [alias],...}

FROM table-name

[WHERE condition]

[GROUP BY columns]

[HAVING group-selection-condition]

[ORDER BY column-names || aliases || column-numbers];

Select Specific Column

SELECT NAME, DEPT_NAME FROM INSTRUCTOR;

Retrieve data For all column using (*):

Arithmetic Expressions:

Arithmetic operators can perform arithmetical operations on numeric

operands involved. Arithmetic operators are addition (+), subtraction (-),

multiplication (*) and division (/). The + and - operators can also be used in

date arithmetic

Use * To Select All Column

SELECT * FROM INSTRUCTOR;

SELECT NAME, DEPT_NAME, SALARY, SALARY/100

FROM INSTRUCTOR;

Null Values:

A null is value is unknown or does not exist

It is NOT the same as a zero or a blank space.

The result of any arithmetic expressions containing a null value is a

Null value.

You cannot use equal operator (=) to compare two null values! Instead, use (IS)

with special keyword null to check if a value is null or not.

Example: Retrieve all student who his grade has not been awarded

The result of an arithmetic expression (involving, for example +, −, ∗, or /) is null if

any of the input values is null

SELECT ID, COURSE_ID,GRADE

FROM TAKES

WHERE GRADE IS NULL;

SELECT NULL*20

FROM DUAL

A Column Alias:

Renames a column heading

Is useful with calculations

Immediately follows the column name (There can also be the optional AS

keyword between the column name and alias.)

Requires double quotation marks if it contains spaces or special characters

or if it is case-sensitive

A Concatenation Operator Links columns or character strings to other columns

Is represented by two vertical bars (|| )

Creates a resultant column that is a character expression

SELECT TIME_SLOT_ID ,Start_HR || ':'||Start_Min as STartTime

,ENd_hr || ':' || End_min as EndTime from Time_slot;

SELECT DISTINCT Statement

SELECT DISTINCT returns only distinct (different) values. SELECT DISTINCT eliminates duplicate records from the results. DISTINCT operates on a single column. DISTINCT for multiple columns is not

supported

SQL WHERE Clause:

To limit the number of rows use the WHERE clause. The WHERE clause filters for rows that meet certain criteria. WHERE is followed by a condition that returns either true or false. WHERE is used with SELECT, UPDATE, and DELETE.

Example: Find the names of all instructors in the Computer Science department

SELECT NAME

FROM INSTRUCTOR

WHERE DEPT_NAME = 'COMP. SCI.';

Notes:

When you deal with character strings or date values, you must enclosed

them by single quotation marks ( ‘ ’ )

Character values are case-sensitive, and date values are format-sensitive.

SQL WHERE LIKE Statement:

Pattern matching can be performed on strings, use the like statement

Patterns are case sensitive

describe patterns by using two special characters

Percent (%): The % character matches any substring

Underscore (_ ): The character matches any character.

Example: Find the names of all student whose name starts with ‘S’.

Example: Find the names of all student whose name with second and third

character “an”

Comparison operators:

Operator Operator Description = Equal to

> Greater than

>= Greater than or equal to

< Less than <= Less than or equal to

<> Not equal to

BETWEEN ... AND... Between two values (inclusive)

IN(set) Match any of a list of values ANY(set) Compare to any value in a set

ALL(set) Compare to all values in a set

[NOT] LIKE Match a character pattern

IS[NOT] NULL Is a null value

Rules of Precedence:

Operator Priority

Parentheses () 1

Arithmetic operators / , * 2

+ , - 3 Concatenation operator || 4

Comparison conditions <,> ,>=, <=,<> 5

IS [NOT] NULL, LIKE, [NOT] IN 6

[NOT] BETWEEN 7 Not equal to 8

NOT logical condition 9

AND logical condition 10

OR logical condition 11

Note: <> all is identical to not in, whereas = all is not the same as in

Example: find the names of instructors with salary amounts between $90,000 and

$100,000.

Instead of:

Example: Find all the names of instructors whose names are neither “Mozart” nor

“Einstein”.

SELECT NAME

FROM INSTRUCTOR

WHERE SALARY BETWEEN 90000 AND 100000;

SELECT NAME

FROM INSTRUCTOR

WHERE SALARY <= 100000 AND SALARY >= 90000;

SELECT DISTINCT NAME

FROM INSTRUCTOR

WHERE NAME NOT IN ('MOZART', 'EINSTEIN');

Sort:

You can sort rows retrieved by a query using the optional [ORDER BY clause].

Example: retrieving all departments’ records sorted by budget.

By default, “ORDER BY” Clause sorts the retrieved rows in ascending order. To reverse the ordering, use “DESC” keyword after column-name.

SELECT DEPT_NAME,BUILDING,BUDGET

FROM DEPARTMENT

ORDER BY BUDGET DESC;

SELECT DEPT_NAME,BUILDING,BUDGET

FROM DEPARTMENT

ORDER BY BUDGET ;

You can also sort rows according to expression result; in this case, you have to use an alias instead of column name also, sort rows according to more than one column.

Example: Find all instructor sorted by their monthly salary.

Example: Find all student sorted by their department name , if there are two student have the same department name , then sort them by total credit in ascending order, then by their “student name” alias.

Sorting According to More Than One Column

SELECT NAME "STUDNET NAME ”,DEPT_NAME,TOT_CRED

FROM STUDENT

ORDER BY DEPT_NAME, TOT_CRED DESC, "STUDNET NAME" ;

SELECT NAME , DEPT_NAME ,SALARY/12 MONTHLY

FROM INSTRUCTOR

ORDER BY MONTHLY

Note: in “ORDER BY” clause, you can type (column | alias) numeric position instead of name.

For example in the previous query, department name column comes first in the query, so its number is 1. Total credit comes second, so its number is 2. Finally, “student name” alias comes third, so its number is 3. Therefore, the previous query can be wrote in another way:

SELECT NAME "STUDNET NAME" ,DEPT_NAME,TOT_CRED

FROM STUDENT

ORDER BY 2,3 DESC, 1 ;

INSERT Statement:

INSERT statement is used to add new rows into a table in the database.

You can also insert new rows without specifying column names, by typing:

“INSERT INTO” table-name VALUES (value-list)”. In this case, you MUST order

values in the same order of its corresponding columns.

Q) Create a section of ‘Database lab CS-348’ course in fall 2016, with sec id of 1

and class room al Quds 218.

Syntax of SQL INSERT Statement

INSERT INTO Table-Name (column_list)

VALUES (values-list);

Example SQL INSERT Statement

INSERT INTO CLASSROOM (BUILDING, ROOM_NUMBER, CAPACITY)

VALUES ('AL QUDS’, 218, 25)

Example SQL INSERT Statement

INSERT INTO CLASSROOM VALUES ('AL QUDS’, 218, 25)

INSERT INTO SECTION

VALUES ('CS-348', 1, 'FALL', 2016, 'AL QUDS', '218', 'A');

Use select with insert statement

Q) Enroll every student in ’ Database CS-347’ course taken in 2009, in the above

section.

DELETE Statement

DELETE statement is used to delete rows from a table according to a specified

condition.

Example:

Note: It also can be used to delete all rows from a table by not specifying any

conditions. If you want to empty a table, you just have to issue this command:

“DELETE FROM table-name”. You should be aware when using this form.

Q) Delete enrollments in the above section where the student’s name is contain

“han” substring

Syntax of SQL DELETE Statement

DELETE FROM table-name

WHERE condition;

Using DELETE Statement

DELETE FROM CLASSROOM

WHERE BUILDING = 'AL QUDS'

INSERT INTO TAKES (ID, COURSE_ID,SEC_ID,SEMESTER,YEAR)

SELECT ID, 'CS-348','1', 'FALL',2016

FROM TAKES

WHERE COURSE_ID='CS-347';

Constant columns

Insert constant value

DELETE FROM TAKES WHERE (ID ,COURSE_ID) IN (

SELECT ID,'CS-348'

FROM STUDENT

WHERE NAME LIKE '%HAN%');

Constant columns

Insert constant value

UPDATE Statement

UPDATE statement is used to modify existing rows values in a table.

Example:

END

Syntax of SQL UPDATE Statement

UPDATE TABLE-NAME

SET COLUMN_NAME_1 = NEW_VALUE1 , COLUMN_NAME_2 = NEW_VALUE2 --

WHERE CONDITION;

Using UPDATE Statement

UPDATE COURSE

SET CREDITS=3

WHERE COURSE_ID='CS-190'