The document is an introduction to SQL that covers the basic SQL statements and concepts. It defines SQL and its uses, including retrieving, inserting, updating, and deleting data from databases. It also covers key SQL statements like SELECT, WHERE, ORDER BY, JOIN, and aggregate functions. The document provides syntax examples for each SQL statement and concept discussed.
4. SQL Intro
What is SQL?
SQL stands for Structured Query Language
SQL lets you access and manipulate databases
SQL is an ANSI (American National Standards Institute) standard
What Can SQL do?
SQL can execute queries against a database
SQL can retrieve data from a database
SQL can insert records in a database
SQL can update records in a database
SQL can delete records from a database
SQL can create new databases
SQL can create new tables in a database
SQL can create stored procedures in a database
SQL can create views in a database
SQL can set permissions on tables, procedures, and views
What is RDBMS?
RDBMS stands for Relational Database Management System.
RDBMS is the basis for SQL, and for all modern database systems such as MS SQL Server,
IBM DB2, Oracle, MySQL, and Microsoft Access.
The data in RDBMS is stored in database objects called tables.
A table is a collection of related data entries and it consists of columns and rows.
SQL
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5. SQL Select
Definition
The SELECT statement is used to select data from a database.
The result is stored in a result table, called the result-set.
Syntax
SELECT column_name
FROM table_name;
Example
SELECT City FROM Customers;
SQL Select Distinct
Definition
The SELECT DISTINCT statement is used to return only distinct
(different) values.
Syntax
SELECT DISTINCT column_name,column_name
FROM table_name;
Example
SELECT DISTINCT City FROM Customers;
SQL Where
Definition
The WHERE clause is used to filter records.
Syntax
SELECT column_name, column_name
FROM table_name
WHERE column_name operator value;
Example
SELECT * FROM Customers
WHERE Country='Mexico';
SQL
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6. SQL And & Or
The AND operator displays a record if both the first condition AND the
Definition
second condition are true.
The OR operator displays a record if either the first condition OR the
second condition is true.
Syntax
SELECT column_name, FROM table_name
WHERE column_name (AND/OR) column_name;
Example
SELECT * FROM Customers
WHERE Country='Germany' AND City='Berlin';
SQL Order By
Definition
Syntax
Example
The ORDER BY keyword is used to sort the result-set by one or more
columns.
SELECT column_name, column_name
FROM table_name
ORDER BY column_name, column_name ASC|DESC;
SELECT * FROM Customers
ORDER BY Country DESC;
SQL Insert Into
Definition
Syntax
Example
SQL
The INSERT INTO statement is used to insert new records in a table.
INSERT INTO table_name
VALUES (value1, value2, value3,...);
INSERT INTO table_name (column1, column2, column3,...)
VALUES (value1, value2, value3,...);
INSERT INTO Customers (CustomerName, City, Country)
VALUES ('Cardinal', 'Stavanger', 'Norway');
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7. SQL Update
Definition
Syntax
Example
The UPDATE statement is used to update existing records in a table.
UPDATE table_name
SET column1=value1, column2=value2,...
WHERE some_column=some_value;
UPDATE Customers
SET ContactName='Alfred Schmidt', City='Hamburg'
WHERE CustomerName='Alfreds Futterkiste';
SQL Delete
Definition
The DELETE statement is used to delete rows in a table.
Syntax
DELETE FROM table_name
WHERE some_column=some_value;
Example
DELETE FROM Customers
WHERE CustomerName='Alfreds Futterkiste' AND
ContactName='Maria Anders';
SQL Select Top
Definition
Syntax
Example
SQL
The SELECT TOP clause is used to specify the number of records to
return.
SELECT TOP number|percent column_name(s)
FROM table_name;
SELECT TOP 2 * FROM Customers;
SELECT TOP 50 PERCENT * FROM Customers;
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8. SQL Select Top
Definition
Syntax
Example
The SELECT TOP clause is used to specify the number of records to
return.
SELECT TOP number|percent column_name(s)
FROM table_name;
SELECT TOP 2 * FROM Customers;
SELECT TOP 50 PERCENT * FROM Customers;
SQL Like
Definition
The LIKE operator is used to search for a specified pattern in a column.
Syntax
SELECT column_name(s)
FROM table_name
WHERE column_name LIKE pattern;
Example
SELECT * FROM Customers
WHERE City LIKE 's%';
SQL Wildcards
Definition
Wildcard characters are used with the SQL LIKE operator. They are used
Syntax
to search for data within a table.
SELECT column_name(s)
FROM table_name
WHERE column_name LIKE pattern;
SELECT * FROM Customers
WHERE City LIKE 'ber%';
Example
SELECT * FROM Customers
WHERE City LIKE '_erlin';
SELECT * FROM Customers
WHERE City LIKE '[!bsp]%';
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9. SQL IN
Definition
The IN operator allows you to specify multiple values in a WHERE clause.
Syntax
SELECT column_name(s)
FROM table_name
WHERE column_name IN (value1,value2,...);
Example
SELECT * FROM Customers
WHERE City IN ('Paris','London');
SQL Between
Definition
The BETWEEN operator selects values within a range. The values can be
Syntax
numbers, text, or dates.
SELECT column_name(s)
FROM table_name
WHERE column_name BETWEEN value1 AND value2;
SELECT * FROM Products
WHERE Price BETWEEN 10 AND 20;
Example
SELECT * FROM Products
WHERE Price NOT BETWEEN 10 AND 20;
SELECT * FROM Orders
WHERE OrderDate BETWEEN #07/04/1996# AND #07/09/1996#;
SQL Join
Definition
Syntax
Example
SQL
An SQL JOIN clause is used to combine rows from two or more tables,
based on a common field between them.
SELECT column_name(s)
FROM table1
JOIN table2
ON table1.column_name=table2.column_name;
SELECT Orders.OrderID, Customers.CustomerName,
Orders.OrderDate
FROM Orders
JOIN Customers
ON Orders.CustomerID=Customers.CustomerID;
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10. SQL Inner Join
The INNER JOIN keyword selects all rows from both tables as long as
Definition
Syntax
Example
there is a match between the columns in both tables. INNER JOIN is
the same as JOIN.
SELECT column_name(s)
FROM table1
JOIN table2
ON table1.column_name=table2.column_name;
SELECT Customers.CustomerName, Orders.OrderID
FROM Customers
INNER JOIN Orders
ON Customers.CustomerID=Orders.CustomerID
ORDER BY Customers.CustomerName;
SQL Left Join
The LEFT JOIN keyword returns all rows from the left table (table1),
Definition
Syntax
Example
with the matching rows in the right table (table2). The result is NULL
in the right side when there is no match.
SELECT column_name(s)
FROM table1
LEFT JOIN table2
ON table1.column_name=table2.column_name;
SELECT Customers.CustomerName, Orders.OrderID
FROM Customers
LEFT JOIN Orders
ON Customers.CustomerID=Orders.CustomerID
ORDER BY Customers.CustomerName;
SQL Right Join
The RIGHT JOIN keyword returns all rows from the right table
Definition
Syntax
Example
SQL
(table2), with the matching rows in the left table (table1). The result
is NULL in the left side when there is no match.
SELECT column_name(s)
FROM table1
RIGHT JOIN table2
ON table1.column_name=table2.column_name;
SELECT Orders.OrderID, Employees.FirstName
FROM Orders
RIGHT JOIN Employees
ON Orders.EmployeeID=Employees.EmployeeID
ORDER BY Orders.OrderID;
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11. SQL Full Join
Definition
Syntax
Example
The FULL OUTER JOIN keyword returns all rows from the left table
(table1) and from the right table (table2).
SELECT column_name(s)
FROM table1
FULL OUTER JOIN table2
ON table1.column_name=table2.column_name;
SELECT Customers.CustomerName, Orders.OrderID
FROM Customers
FULL OUTER JOIN Orders
ON Customers.CustomerID=Orders.CustomerID
ORDER BY Customers.CustomerName;
SQL Union
Definition
Syntax
Example
The SQL UNION operator combines the result of two or more SELECT
statements.
SELECT column_name(s) FROM table1
UNION
SELECT column_name(s) FROM table2;
SELECT City FROM Customers
UNION
SELECT City FROM Suppliers
ORDER BY City;
SQL Select Into
Definition
Syntax
Example
SQL
The SELECT INTO statement selects data from one table and inserts it
into a new table.
SELECT *
INTO newtable [IN externaldb]
FROM table1;
SELECT *
INTO CustomersBackup2013
FROM Customers;
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12. SQL Insert Into Select
Definition
Syntax
Example
The INSERT INTO SELECT statement copies data from one table and
inserts it into an existing table.
INSERT INTO table2
SELECT * FROM table1;
INSERT INTO table2
(column_name(s))
SELECT column_name(s)
FROM table1;
INSERT INTO Customers (CustomerName, Country)
SELECT SupplierName, Country FROM Suppliers;
INSERT INTO Customers (CustomerName, Country)
SELECT SupplierName, Country FROM Suppliers
WHERE Country='Germany';
SQL Create Database
Definition
The CREATE DATABASE statement is used to create a database.
Syntax
CREATE DATABASE dbname;
Example
CREATE DATABASE my_db;
SQL Create Table
The CREATE TABLE statement is used to create a table in a database.
Definition
Syntax
SQL
Tables are organized into rows and columns; and each table must have a
name.
CREATE TABLE table_name
(
column_name1 data_type(size),
column_name2 data_type(size),
column_name3 data_type(size),
....
);
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13. Example
CREATE TABLE Persons
(
PersonID int,
LastName varchar(255),
FirstName varchar(255),
Address varchar(255),
City varchar(255)
);
SQL Constraints
Definition
Syntax
Example
SQL constraints are used to specify rules for the data in a table.
CREATE TABLE table_name
(
column_name1 data_type(size) constraint_name,
column_name2 data_type(size) constraint_name,
column_name3 data_type(size) constraint_name,
....
);
NOT NULL- Indicates that a column cannot store NULL value.
UNIQUE- Ensures that each row for a column must have a unique
value.
PRIMARY KEY- A combination of a NOT NULL and UNIQUE. Ensures
that a column (or combination of two or more columns) have an
unique identity which helps to find a particular record in a
table more easily and quickly.
FOREIGN KEY- Ensure the referential integrity of the data in
one table to match values in another table
CHECK- Ensures that the value in a column meets a specific
condition.
DEFAULT- Specifies a default value when specified none for
this column.
SQL Not Null
Definition
Example
SQL
The NOT NULL constraint enforces a column to NOT accept NULL
values.
CREATE TABLE Persons NotNull
(
P_Id int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255)
)
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14. SQL Unique
Definition
Example
The UNIQUE constraint uniquely identifies each record in a database
table.
CREATE TABLE Persons Unique
(
P_Id int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255),
UNIQUE (P_Id)
)
SQL Primary Key
The PRIMARY KEY constraint uniquely identifies each record in a
database table.
Definition
Primary keys must contain unique values.
A primary key column cannot contain NULL values.
Each table should have a primary key, and each table can have only ONE
Example
SQL
primary key.
CREATE TABLE Persons
(
P_Id int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255),
PRIMARY KEY (P_Id)
)
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15. SQL Foreign Key
Definition
Example
A FOREIGN KEY in one table points to a PRIMARY KEY in another
table.
CREATE TABLE Orders
(
O_Id int NOT NULL,
OrderNo int NOT NULL,
P_Id int,
PRIMARY KEY (O_Id),
FOREIGN KEY (P_Id) REFERENCES Persons(P_Id)
)
SQL Check
Definition
Example
The CHECK constraint is used to limit the value range that can be
placed in a column.
CREATE TABLE Persons
(
P_Id int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255),
CHECK (P_Id>0)
)
SQL Default
The DEFAULT constraint is used to insert a default value into a column.
Definition
Example
SQL
The default value will be added to all new records, if no other value is
specified.
CREATE TABLE Persons
(
P_Id int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Address varchar(255),
City varchar(255),
CHECK (P_Id>0)
)
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16. SQL Create Index
The CREATE INDEX statement is used to create indexes in tables.
Definition
Indexes allow the database application to find data fast; without reading
the whole table.
Syntax
CREATE INDEX index_name
ON table_name (column_name)
Example
CREATE INDEX PIndex
ON Persons (LastName)
SQL Drop
The DROP statement is used to delete a table or database.
Definition
Syntax
Example
TRANCATE statement is when we only want to delete the data inside
the table, and not the table itself.
DROP TABLE table_name
DROP DATABASE database_name
TRUNCATE TABLE table_name
DROP TABLE Person
DROP DATABASE test
Truncate TABLE Person
SQL Alter
Definition
The ALTER TABLE statement is used to add, delete, or modify columns
Syntax
ALTER TABLE table_name
ADD column_name datatype
Example
ALTER TABLE Persons
DROP COLUMN DateOfBirth
SQL
in an existing table.
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17. SQL Null
NULL values represent missing unknown data.
Definition
By default, a table column can hold NULL values.
Note: It is not possible to compare NULL and 0; they are not
Syntax
Example
SQL
equivalent.
SELECT column_name FROM table
WHERE column_name IS NULL
SELECT column_name FROM table
WHERE column_name IS NOT NULL
SELECT LastName,FirstName,Address FROM Persons
WHERE Address IS NULL
SELECT LastName,FirstName,Address FROM Persons
WHERE Address IS NOT NULL
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18. SQL General Data Types
Database Type
Description
CHARACTER(n)
Character string. Fixed-length n
VARCHAR(n) or
CHARACTER VARYING(n)
BINARY(n)
Character string. Variable length. Maximum
length n
Binary string. Fixed-length n
BOOLEAN
Stores TRUE or FALSE values
VARBINARY(n) or
BINARY VARYING(n)
INTEGER(p)
Binary string. Variable length. Maximum length
n
Integer numerical (no decimal). Precision p
SMALLINT
Integer numerical (no decimal). Precision 5
INTEGER
Integer numerical (no decimal). Precision 10
BIGINT
Integer numerical (no decimal). Precision 19
DECIMAL(p,s)
REAL
Exact numerical, precision p, scale s. Example:
decimal(5,2) is a number that has 3 digits
before the decimal and 2 digits after the
decimal
Exact numerical, precision p, scale s. (Same as
DECIMAL)
Approximate numerical, mantissa precision p. A
floating number in base 10 exponential
notation. The size argument for this type
consists of a single number specifying the
minimum precision
Approximate numerical, mantissa precision 7
FLOAT
Approximate numerical, mantissa precision 16
DOUBLE PRECISION
Approximate numerical, mantissa precision 16
DATE
Stores year, month, and day values
TIME
Stores hour, minute, and second values
TIMESTAMP
Stores year, month, day, hour, minute, and
second values
Composed of a number of integer fields,
representing a period of time, depending on the
type of interval
A set-length and ordered collection of elements
NUMERIC(p,s)
FLOAT(p)
INTERVAL
ARRAY
MULTISET
XML
SQL
A variable-length and unordered collection of
elements
Stores XML data
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