9 Introduction to SQL Part I
INTRODUCTION TO SQL
Presented by :
Satrio Agung Wicaksono
DEFINITION
Structured Query Language (SQL) is a high-level
language that allows users to manipulate
relational data
One of the strengths of SQL is that users need
only specify the information they need without
having to know how to retrieve it
THREE SQL CATEGORIES
DDL – Data definition language used to define,
change, or drop database objects
DML – Data manipulation language used to read
and modify data
DCL – Data control language used to grant and
revoke authorizations
HISTORY OF SQL
Don Chamberlin and Ray Boyce from IBM
Corporation developed the SQL language in the
1970's as part of the System R project; a project
established to provide a practical implementation
to Codd's relational model
Originally, the language was termed “Structured
English Query Language” or SEQUEL, but it was
later changed to SQL as SEQUEL was a registered
trademark of a UK based company
SQL was adopted as a standard language in 1986
by the American National Standards Institute
(ANSI) and by the International Standards
Organization (ISO) in 1987.
DEFINING A RELATIONAL
DATABASE SCHEMA IN SQL
Data Types
Like any programming language, databases also
support a limited set of data types, which can be used
to define the types of data a column can store.
Basic data types include integer, float, decimal, char,
date, time, blob, and so on
DATES AND TIMES DATA TYPES
All databases support various date and time specific data types
and functions
DB2 has the following data types for date and time. :
Date (YYYY-MM-DD)
Time (HH:MM:SS)
Timestamp (YYYY-MM-DD-HH:MM:SS:ssssss)
The following, is a partial set of functions specialized for date
and time:
Year
Month
Day
Dayname
Hour
Minute
Second
Microsecond
CREATING A TABLE
A table is a data set, organized and stored in
rows and columns.
A table holds data for like items, for example
students, professors, subjects, books etc
Entities in a data model generally map to tables
when implemented in databases. Attributes of
entities map to columns of the table
example:
create table myTable (col1 integer)
DEFAULT VALUES
When data is inserted into a table, you may want to automatically generate default values for a
few columns
Using default value :
To define a column that will generate a department number as an incremented value of the last
department number
NULL VALUES
A NULL represents an unknown state
For example, a table that stores the course marks of
students can allow for NULL values. This could mean
to the teacher that the student did not submit an
assignment, or did not take an exam. It is different
from a mark of zero, where a student did take the
exam, but failed on all the questions
when you don't want a NULL to be allowed. For
example, if the country field is required for your
application, ensure you prevent NULL values as
follows
create table myTable (name varchar(30), country
varchar(20) NOT NULL)
CONSTRAINTS
Constraints allow you to define rules for the data in
your table. There are different types of constraints:
A UNIQUE constraint prevents duplicate values in a table.
This is implemented using unique indexes and is specified
in the CREATE TABLE statement using the keyword
UNIQUE. A NULL is part of the UNIQUE data values
domain.
A PRIMARY KEY constraint is similar to a UNIQUE
constraint, however it excludes NULL as valid data.
Primary keys always have an index associated with it.
A REFERENTIAL constraint is used to support referential
integrity which allows you to manage relationships between
tables. This is discussed in more detail in the next section.
A CHECK constraint ensures the values you enter into a
column are within the rules specified in the constraint.
CONSTRAINTS, CONT’D…
The following example shows a table definition
with several CHECK constraints and a
PRIMARY KEY defined:
REFERENTIAL INTEGRITY
Referential integrity establishes relationships
between tables.
Using a combination of primary keys and foreign
keys, it can enforce the validity of your data.
Referential integrity reduces application code
complexity by eliminating the need to place data
level referential validation at the application
level.
Only tables that have columns defined as
UNIQUE or PRIMARY KEY can be referenced in
other tables as foreign keys for referential
integrity
REFERENTIAL INTEGRITY,
CONT’D…
Referential integrity can be defined during table definition or after the
table has been created as shown in the example below where three
different syntaxes are illustrated:
Sintax 1 :
CREATE TABLE DEPENDANT_TABLE
(ID INTEGER REFERENCES BASE_TABLE(UNIQUE_OR_PRIMARY_KEY),
NAME VARCHAR(9),
:
:
:
);
Sintax 2 :
CREATE TABLE DEPENDANT_TABLE
(ID INTEGER,
NAME VARCHAR(9),
:
:
:,
CONSTRAINT constraint_name FOREIGN KEY (ID)
REFERENCES BASE_TABLE(UNIQUE_OR_PRIMARY_KEY)
);
REFERENTIAL INTEGRITY,
CONT’D…
Sintak 3:
CREATE TABLE DEPENDANT_TABLE
(ID INTEGER,
NAME VARCHAR(9),
:
:
:
);
ALTER TABLE DEPENDANT_TABLE
ADD CONSTRAINT constraint_name FOREIGN
KEY (ID)
REFERENCES
BASE_TABLE(UNIQUE_OR_PRIMARY_KEY);
REFERENTIAL INTEGRITY,
CONT’D…
There are different rules to handle deletes and updates and the behavior
depends on the following constructs used when defining the tables:
CASCADE
SET NULL
With this option no action is performed as long as referential integrity is maintained before and
after the statement execution.
RESTRICT
With this option all the referring cells in dependant tables are set to NULL
NO ACTION
As the name suggests, with the cascade option the operation is cascaded to all rows in the
dependant tables that are referencing the row or value to be modified or deleted in the base table.
With this option, the update or delete of rows having references to dependant tables are not
allowed to continue
The statement below shows where the delete and update rules are specified:
ALTER TABLE DEPENDANT_TABLE
ADD CONSTRAINT constraint_name
FOREIGN KEY column_name
ON DELETE
ON UPDATE ;
A delete action type can be a CASCADE, SET NULL, NO ACTION, or
RESTRICT. An update action type can be a NO ACT ON, or RESTRICT
CREATING A SCHEMA
Just in the same way we store and manage data
files on a computer in directories or folders and
keep related or similar files together;
a schema in DB2 is a database object that allows
you to group related database objects together.
In DB2, every object has two parts, a schema
name, and the name of the object
CREATING A SCHEMA , CONT’D…
To create a schema, use this statement:
To create a table with the above schema, explicitly
include it in the CREATE TABLE statement as
follows:
create schema mySchema
create table mySchema.myTable (col1 integer)
When the schema is not specified, DB2 uses an
implicit schema, which is typically the user ID
used to connect to the database. You can also
change the implicit schema for your current
session with the SET CURRENT SCHEMA
command as follows:
set current schema mySchema
MODIFYING DATABASE OBJECTS
Once a database object is created, it may be
necessary to change its properties to suit
changing business requirements.
Dropping and recreating the object is one way to
achieve this modification; however, dropping the
object has severe side effects.
A better way to modify database objects is to use
the ALTER SQL statement. For example,
assuming you would like to change a table
definition so that NULLs are not allowed for a
given column, you can try this SQL statement:
alter table myTable alter column col1 set not null
RENAMING DATABASE OBJECTS
Once database objects are created, they can be
renamed using the SQL statement, RENAME. To
rename any database object use the following SQL
syntax:
RENAME to
Where the object type can be for example, a table,
table space, or index. Not all database objects can
be renamed after they are created.
To rename a column, the ALTER TABLE SQL
statement should be used in conjunction with
RENAME. For example:
ALTER TABLE RENAME COLUMN
TO
DROPING DATABASE TABLE
DROP TABLE statement allows you to remove
tables from your schema:
DROP TABLE SCHEMA.TABLE_NAME
Ex : DROP TABLE DB2ADMIN.EMPLOYEE
DATA MANIPULATION WITH SQL
Selecting Data
Inserting Data
Deleting Data
Updating Data
EMPLOYEE TABLE - PART 1 (1 OF 2)
EMPLOYEE TABLE - PART 1 (2 OF 2)
DEPARTMENT TABLE
PROJECT TABLE
STRUCTURE OF AN SQL QUERY
SELECT - Defines result columns
Column names
Arithmetic expressions
Literals (text or numeric)
Scalar functions
Column functions
Concatenation
FROM - Table or view names
WHERE - Conditions (qualifies rows)
ORDER BY - Sorts result rows
RETRIEVING ALL COLUMNS, ALL
ROWS
RETRIEVING ALL COLUMNS,
LIMITED ROWS
SELECTING SPECIFIC COLUMNS
SELECT WITH ORDERED OUTPUT (1
OF 2)
SELECT WITH ORDERED OUTPUT (2
OF 2)
ALTERNATE ORDER BY
SPECIFICATIONS
SELECT LASTNAME, FIRSTNME, WORKDEPT,
JOB, SEX FROM EMPLOYEE ORDER BY
WORKDEPT DESC, JOB, LASTNAME, SEX
DESC
Equivalent ORDER BY clauses:
ORDER BY WORKDEPT DESC, JOB ASC,
LASTNAME ASC, SEX DESC
ORDER BY 3 DESC, 4, 1, 5 DESC
ORDER BY 3 DESC, 4 ASC, 1 ASC, 5 DESC
ORDER BY 3 DESC, JOB, LASTNAME, 5 DESC
ORDER BY WORKDEPT DESC, 4 ASC, 1 ASC,
SEX DESC
SUPPRESSING DUPLICATE OUTPUT
ROWS (1 OF 2)
SUPPRESSING DUPLICATE OUTPUT
ROWS (2 OF 2)
RETRIEVING ROWS BY CHARACTER
COMPARISON
RETRIEVING ROWS BY NUMERICAL
COMPARISON
COMPARISON OPERATORS
SELECT *
FROM EMPLOYEE
WHERE SALARY = 20000 -- equal to
OR SALARY 20000 -- not equal to
OR SALARY > 20000 -- greater than
OR SALARY >= 20000 -- greater than or
equal to
OR SALARY < 20000 -- less than
OR SALARY
Presented by :
Satrio Agung Wicaksono
DEFINITION
Structured Query Language (SQL) is a high-level
language that allows users to manipulate
relational data
One of the strengths of SQL is that users need
only specify the information they need without
having to know how to retrieve it
THREE SQL CATEGORIES
DDL – Data definition language used to define,
change, or drop database objects
DML – Data manipulation language used to read
and modify data
DCL – Data control language used to grant and
revoke authorizations
HISTORY OF SQL
Don Chamberlin and Ray Boyce from IBM
Corporation developed the SQL language in the
1970's as part of the System R project; a project
established to provide a practical implementation
to Codd's relational model
Originally, the language was termed “Structured
English Query Language” or SEQUEL, but it was
later changed to SQL as SEQUEL was a registered
trademark of a UK based company
SQL was adopted as a standard language in 1986
by the American National Standards Institute
(ANSI) and by the International Standards
Organization (ISO) in 1987.
DEFINING A RELATIONAL
DATABASE SCHEMA IN SQL
Data Types
Like any programming language, databases also
support a limited set of data types, which can be used
to define the types of data a column can store.
Basic data types include integer, float, decimal, char,
date, time, blob, and so on
DATES AND TIMES DATA TYPES
All databases support various date and time specific data types
and functions
DB2 has the following data types for date and time. :
Date (YYYY-MM-DD)
Time (HH:MM:SS)
Timestamp (YYYY-MM-DD-HH:MM:SS:ssssss)
The following, is a partial set of functions specialized for date
and time:
Year
Month
Day
Dayname
Hour
Minute
Second
Microsecond
CREATING A TABLE
A table is a data set, organized and stored in
rows and columns.
A table holds data for like items, for example
students, professors, subjects, books etc
Entities in a data model generally map to tables
when implemented in databases. Attributes of
entities map to columns of the table
example:
create table myTable (col1 integer)
DEFAULT VALUES
When data is inserted into a table, you may want to automatically generate default values for a
few columns
Using default value :
To define a column that will generate a department number as an incremented value of the last
department number
NULL VALUES
A NULL represents an unknown state
For example, a table that stores the course marks of
students can allow for NULL values. This could mean
to the teacher that the student did not submit an
assignment, or did not take an exam. It is different
from a mark of zero, where a student did take the
exam, but failed on all the questions
when you don't want a NULL to be allowed. For
example, if the country field is required for your
application, ensure you prevent NULL values as
follows
create table myTable (name varchar(30), country
varchar(20) NOT NULL)
CONSTRAINTS
Constraints allow you to define rules for the data in
your table. There are different types of constraints:
A UNIQUE constraint prevents duplicate values in a table.
This is implemented using unique indexes and is specified
in the CREATE TABLE statement using the keyword
UNIQUE. A NULL is part of the UNIQUE data values
domain.
A PRIMARY KEY constraint is similar to a UNIQUE
constraint, however it excludes NULL as valid data.
Primary keys always have an index associated with it.
A REFERENTIAL constraint is used to support referential
integrity which allows you to manage relationships between
tables. This is discussed in more detail in the next section.
A CHECK constraint ensures the values you enter into a
column are within the rules specified in the constraint.
CONSTRAINTS, CONT’D…
The following example shows a table definition
with several CHECK constraints and a
PRIMARY KEY defined:
REFERENTIAL INTEGRITY
Referential integrity establishes relationships
between tables.
Using a combination of primary keys and foreign
keys, it can enforce the validity of your data.
Referential integrity reduces application code
complexity by eliminating the need to place data
level referential validation at the application
level.
Only tables that have columns defined as
UNIQUE or PRIMARY KEY can be referenced in
other tables as foreign keys for referential
integrity
REFERENTIAL INTEGRITY,
CONT’D…
Referential integrity can be defined during table definition or after the
table has been created as shown in the example below where three
different syntaxes are illustrated:
Sintax 1 :
CREATE TABLE DEPENDANT_TABLE
(ID INTEGER REFERENCES BASE_TABLE(UNIQUE_OR_PRIMARY_KEY),
NAME VARCHAR(9),
:
:
:
);
Sintax 2 :
CREATE TABLE DEPENDANT_TABLE
(ID INTEGER,
NAME VARCHAR(9),
:
:
:,
CONSTRAINT constraint_name FOREIGN KEY (ID)
REFERENCES BASE_TABLE(UNIQUE_OR_PRIMARY_KEY)
);
REFERENTIAL INTEGRITY,
CONT’D…
Sintak 3:
CREATE TABLE DEPENDANT_TABLE
(ID INTEGER,
NAME VARCHAR(9),
:
:
:
);
ALTER TABLE DEPENDANT_TABLE
ADD CONSTRAINT constraint_name FOREIGN
KEY (ID)
REFERENCES
BASE_TABLE(UNIQUE_OR_PRIMARY_KEY);
REFERENTIAL INTEGRITY,
CONT’D…
There are different rules to handle deletes and updates and the behavior
depends on the following constructs used when defining the tables:
CASCADE
SET NULL
With this option no action is performed as long as referential integrity is maintained before and
after the statement execution.
RESTRICT
With this option all the referring cells in dependant tables are set to NULL
NO ACTION
As the name suggests, with the cascade option the operation is cascaded to all rows in the
dependant tables that are referencing the row or value to be modified or deleted in the base table.
With this option, the update or delete of rows having references to dependant tables are not
allowed to continue
The statement below shows where the delete and update rules are specified:
ALTER TABLE DEPENDANT_TABLE
ADD CONSTRAINT constraint_name
FOREIGN KEY column_name
ON DELETE
ON UPDATE ;
A delete action type can be a CASCADE, SET NULL, NO ACTION, or
RESTRICT. An update action type can be a NO ACT ON, or RESTRICT
CREATING A SCHEMA
Just in the same way we store and manage data
files on a computer in directories or folders and
keep related or similar files together;
a schema in DB2 is a database object that allows
you to group related database objects together.
In DB2, every object has two parts, a schema
name, and the name of the object
CREATING A SCHEMA , CONT’D…
To create a schema, use this statement:
To create a table with the above schema, explicitly
include it in the CREATE TABLE statement as
follows:
create schema mySchema
create table mySchema.myTable (col1 integer)
When the schema is not specified, DB2 uses an
implicit schema, which is typically the user ID
used to connect to the database. You can also
change the implicit schema for your current
session with the SET CURRENT SCHEMA
command as follows:
set current schema mySchema
MODIFYING DATABASE OBJECTS
Once a database object is created, it may be
necessary to change its properties to suit
changing business requirements.
Dropping and recreating the object is one way to
achieve this modification; however, dropping the
object has severe side effects.
A better way to modify database objects is to use
the ALTER SQL statement. For example,
assuming you would like to change a table
definition so that NULLs are not allowed for a
given column, you can try this SQL statement:
alter table myTable alter column col1 set not null
RENAMING DATABASE OBJECTS
Once database objects are created, they can be
renamed using the SQL statement, RENAME. To
rename any database object use the following SQL
syntax:
RENAME to
Where the object type can be for example, a table,
table space, or index. Not all database objects can
be renamed after they are created.
To rename a column, the ALTER TABLE SQL
statement should be used in conjunction with
RENAME. For example:
ALTER TABLE RENAME COLUMN
TO
DROPING DATABASE TABLE
DROP TABLE statement allows you to remove
tables from your schema:
DROP TABLE SCHEMA.TABLE_NAME
Ex : DROP TABLE DB2ADMIN.EMPLOYEE
DATA MANIPULATION WITH SQL
Selecting Data
Inserting Data
Deleting Data
Updating Data
EMPLOYEE TABLE - PART 1 (1 OF 2)
EMPLOYEE TABLE - PART 1 (2 OF 2)
DEPARTMENT TABLE
PROJECT TABLE
STRUCTURE OF AN SQL QUERY
SELECT - Defines result columns
Column names
Arithmetic expressions
Literals (text or numeric)
Scalar functions
Column functions
Concatenation
FROM - Table or view names
WHERE - Conditions (qualifies rows)
ORDER BY - Sorts result rows
RETRIEVING ALL COLUMNS, ALL
ROWS
RETRIEVING ALL COLUMNS,
LIMITED ROWS
SELECTING SPECIFIC COLUMNS
SELECT WITH ORDERED OUTPUT (1
OF 2)
SELECT WITH ORDERED OUTPUT (2
OF 2)
ALTERNATE ORDER BY
SPECIFICATIONS
SELECT LASTNAME, FIRSTNME, WORKDEPT,
JOB, SEX FROM EMPLOYEE ORDER BY
WORKDEPT DESC, JOB, LASTNAME, SEX
DESC
Equivalent ORDER BY clauses:
ORDER BY WORKDEPT DESC, JOB ASC,
LASTNAME ASC, SEX DESC
ORDER BY 3 DESC, 4, 1, 5 DESC
ORDER BY 3 DESC, 4 ASC, 1 ASC, 5 DESC
ORDER BY 3 DESC, JOB, LASTNAME, 5 DESC
ORDER BY WORKDEPT DESC, 4 ASC, 1 ASC,
SEX DESC
SUPPRESSING DUPLICATE OUTPUT
ROWS (1 OF 2)
SUPPRESSING DUPLICATE OUTPUT
ROWS (2 OF 2)
RETRIEVING ROWS BY CHARACTER
COMPARISON
RETRIEVING ROWS BY NUMERICAL
COMPARISON
COMPARISON OPERATORS
SELECT *
FROM EMPLOYEE
WHERE SALARY = 20000 -- equal to
OR SALARY 20000 -- not equal to
OR SALARY > 20000 -- greater than
OR SALARY >= 20000 -- greater than or
equal to
OR SALARY < 20000 -- less than
OR SALARY