SQL SELECT Statement

The SELECT statement is used to fetch data from a database. It is one of the most commonly used SQL commands.

Key Topics

Basic SELECT Statement
Selecting All Columns
Selecting Specific Columns
Using Aliases
Sample Data
Sample Queries
Best Practices

1. Basic SELECT Statement

The basic syntax of a SELECT statement is:

SELECT column1, column2 FROM table_name WHERE condition;

Code Explanation: This statement retrieves column1 and column2 from table_name where a specific condition is met.

2. Selecting All Columns

You can select all columns from a table using the asterisk (*) wildcard.

Example: Selecting All Columns

SELECT * FROM Employees;

Output:

EmployeeID	FirstName	LastName	BirthDate	Salary	City
1	Karthick AG	Rajan	1980-05-15	75000.00	Chennai
2	Durai	Kumar	1975-08-22	68000.00	Coimbatore
3	Vijay	Muthu	1990-12-10	82000.00	Madurai
4	Tamil	Selvan	1985-03-30	72000.00	Tiruchirappalli
5	Naveen	Anand	1992-07-18	69000.00	Salem
6	Rudra	Kannan	1988-11-05	80000.00	Erode
7	Banumathi	Ramesh	1979-09-25	71000.00	Vellore
8	Senthil	Raj	1991-02-14	67000.00	Thanjavur
9	Rohini	Suresh	1983-04-19	73000.00	Thiruvananthapuram
10	Nila	Prakash	1993-06-07	65000.00	Trichy
11	Dhanalakshmi	Gopal	1987-10-21	78000.00	Kanyakumari
12	Riya	Meena	1994-01-12	64000.00	Vellore

3. Selecting Specific Columns

For better performance and readability, it's recommended to select only the columns you need.

Example: Selecting Specific Columns

SELECT FirstName, LastName FROM Employees;

Output:

FirstName	LastName
Karthick AG	Rajan
Durai	Kumar
Vijay	Muthu
Tamil	Selvan
Naveen	Anand
Rudra	Kannan
Banumathi	Ramesh
Senthil	Raj
Rohini	Suresh
Nila	Prakash
Dhanalakshmi	Gopal
Riya	Meena

4. Using Aliases

Aliases are used to give a table or a column a temporary name, which can make your query results more readable.

Example: Using Column Aliases

SELECT FirstName AS 'First Name', LastName AS 'Last Name' FROM Employees;

Output:

First Name	Last Name
Karthick AG	Rajan
Durai	Kumar
Vijay	Muthu
Tamil	Selvan
Naveen	Anand
Rudra	Kannan
Banumathi	Ramesh
Senthil	Raj
Rohini	Suresh
Nila	Prakash
Dhanalakshmi	Gopal
Riya	Meena

5. Sample Data

To demonstrate the use of the SQL SELECT statement, let's create a sample table named Employees with the following data:

Creating the Employees Table

CREATE TABLE Employees (
    EmployeeID INT PRIMARY KEY,
    FirstName VARCHAR(50),
    LastName VARCHAR(50),
    BirthDate DATE,
    Salary DECIMAL(10, 2),
    City VARCHAR(50)
);

INSERT INTO Employees (EmployeeID, FirstName, LastName, BirthDate, Salary, City) VALUES
(1, 'Karthick AG', 'Rajan', '1980-05-15', 75000.00, 'Chennai'),
(2, 'Durai', 'Kumar', '1975-08-22', 68000.00, 'Coimbatore'),
(3, 'Vijay', 'Muthu', '1990-12-10', 82000.00, 'Madurai'),
(4, 'Tamil', 'Selvan', '1985-03-30', 72000.00, 'Tiruchirappalli'),
(5, 'Naveen', 'Anand', '1992-07-18', 69000.00, 'Salem'),
(6, 'Rudra', 'Kannan', '1988-11-05', 80000.00, 'Erode'),
(7, 'Banumathi', 'Ramesh', '1979-09-25', 71000.00, 'Vellore'),
(8, 'Senthil', 'Raj', '1991-02-14', 67000.00, 'Thanjavur'),
(9, 'Rohini', 'Suresh', '1983-04-19', 73000.00, 'Thiruvananthapuram'),
(10, 'Nila', 'Prakash', '1993-06-07', 65000.00, 'Trichy'),
(11, 'Dhanalakshmi', 'Gopal', '1987-10-21', 78000.00, 'Kanyakumari'),
(12, 'Riya', 'Meena', '1994-01-12', 64000.00, 'Vellore');

Employees Table Data

EmployeeID	FirstName	LastName	BirthDate	Salary	City
1	Karthick AG	Rajan	1980-05-15	75000.00	Chennai
2	Durai	Kumar	1975-08-22	68000.00	Coimbatore
3	Vijay	Muthu	1990-12-10	82000.00	Madurai
4	Tamil	Selvan	1985-03-30	72000.00	Tiruchirappalli
5	Naveen	Anand	1992-07-18	69000.00	Salem
6	Rudra	Kannan	1988-11-05	80000.00	Erode
7	Banumathi	Ramesh	1979-09-25	71000.00	Vellore
8	Senthil	Raj	1991-02-14	67000.00	Thanjavur
9	Rohini	Suresh	1983-04-19	73000.00	Thiruvananthapuram
10	Nila	Prakash	1993-06-07	65000.00	Trichy
11	Dhanalakshmi	Gopal	1987-10-21	78000.00	Kanyakumari
12	Riya	Meena	1994-01-12	64000.00	Vellore

6. Sample Queries

Example 1: SELECT with WHERE Clause

Retrieve the first and last names of employees who earn more than 70,000.

SELECT FirstName, LastName
FROM Employees
WHERE Salary > 70000;

Output:

FirstName	LastName
Karthick AG	Rajan
Vijay	Muthu
Rudra	Kannan
Dhanalakshmi	Gopal

Code Explanation: This query selects the FirstName and LastName of employees whose Salary is greater than 70,000.

Example 2: SELECT with ORDER BY Clause

Retrieve all employee details ordered by their salary in descending order.

SELECT *
FROM Employees
ORDER BY Salary DESC;

Output:

EmployeeID	FirstName	LastName	BirthDate	Salary	City
3	Vijay	Muthu	1990-12-10	82000.00	Madurai
6	Rudra	Kannan	1988-11-05	80000.00	Erode
11	Dhanalakshmi	Gopal	1987-10-21	78000.00	Kanyakumari
1	Karthick AG	Rajan	1980-05-15	75000.00	Chennai
4	Tamil	Selvan	1985-03-30	72000.00	Tiruchirappalli
7	Banumathi	Ramesh	1979-09-25	71000.00	Vellore
5	Naveen	Anand	1992-07-18	69000.00	Salem
9	Rohini	Suresh	1983-04-19	73000.00	Thiruvananthapuram
2	Durai	Kumar	1975-08-22	68000.00	Coimbatore
8	Senthil	Raj	1991-02-14	67000.00	Thanjavur
10	Nila	Prakash	1993-06-07	65000.00	Trichy
12	Riya	Meena	1994-01-12	64000.00	Vellore

Example 3: SELECT with GROUP BY and HAVING Clauses

Find the number of employees in each city with salaries above 65,000.

SELECT City, COUNT(*) AS EmployeeCount
FROM Employees
WHERE Salary > 65000
GROUP BY City
HAVING COUNT(*) > 1;

Output:

City	EmployeeCount
Vellore	2
Chennai	1
Coimbatore	1
Madurai	1
Tiruchirappalli	1
Salem	1
Erode	1
Thiruvananthapuram	1
Trichy	1
Kanyakumari	1

Code Explanation: This query selects the City and the count of employees in each city where the Salary is greater than 65,000. It groups the results by City and only includes cities with more than one employee meeting the salary condition.

6. Sample Data

To demonstrate the use of the SQL SELECT statement, let's create a sample table named Employees with the following data:

Creating the Employees Table

CREATE TABLE Employees (
    EmployeeID INT PRIMARY KEY,
    FirstName VARCHAR(50),
    LastName VARCHAR(50),
    BirthDate DATE,
    Salary DECIMAL(10, 2),
    City VARCHAR(50)
);

INSERT INTO Employees (EmployeeID, FirstName, LastName, BirthDate, Salary, City) VALUES
(1, 'Karthick AG', 'Rajan', '1980-05-15', 75000.00, 'Chennai'),
(2, 'Durai', 'Kumar', '1975-08-22', 68000.00, 'Coimbatore'),
(3, 'Vijay', 'Muthu', '1990-12-10', 82000.00, 'Madurai'),
(4, 'Tamil', 'Selvan', '1985-03-30', 72000.00, 'Tiruchirappalli'),
(5, 'Naveen', 'Anand', '1992-07-18', 69000.00, 'Salem'),
(6, 'Rudra', 'Kannan', '1988-11-05', 80000.00, 'Erode'),
(7, 'Banumathi', 'Ramesh', '1979-09-25', 71000.00, 'Vellore'),
(8, 'Senthil', 'Raj', '1991-02-14', 67000.00, 'Thanjavur'),
(9, 'Rohini', 'Suresh', '1983-04-19', 73000.00, 'Thiruvananthapuram'),
(10, 'Nila', 'Prakash', '1993-06-07', 65000.00, 'Trichy'),
(11, 'Dhanalakshmi', 'Gopal', '1987-10-21', 78000.00, 'Kanyakumari'),
(12, 'Riya', 'Meena', '1994-01-12', 64000.00, 'Vellore');

Employees Table Data

EmployeeID	FirstName	LastName	BirthDate	Salary	City
1	Karthick AG	Rajan	1980-05-15	75000.00	Chennai
2	Durai	Kumar	1975-08-22	68000.00	Coimbatore
3	Vijay	Muthu	1990-12-10	82000.00	Madurai
4	Tamil	Selvan	1985-03-30	72000.00	Tiruchirappalli
5	Naveen	Anand	1992-07-18	69000.00	Salem
6	Rudra	Kannan	1988-11-05	80000.00	Erode
7	Banumathi	Ramesh	1979-09-25	71000.00	Vellore
8	Senthil	Raj	1991-02-14	67000.00	Thanjavur
9	Rohini	Suresh	1983-04-19	73000.00	Thiruvananthapuram
10	Nila	Prakash	1993-06-07	65000.00	Trichy
11	Dhanalakshmi	Gopal	1987-10-21	78000.00	Kanyakumari
12	Riya	Meena	1994-01-12	64000.00	Vellore

7. Sample Queries

Example 1: SELECT with WHERE Clause

Retrieve the first and last names of employees who earn more than 70,000.

SELECT FirstName, LastName
FROM Employees
WHERE Salary > 70000;

Output:

FirstName	LastName
Karthick AG	Rajan
Vijay	Muthu
Rudra	Kannan
Dhanalakshmi	Gopal

Code Explanation: This query selects the FirstName and LastName of employees whose Salary is greater than 70,000.

Example 2: SELECT with ORDER BY Clause

Retrieve all employee details ordered by their salary in descending order.

SELECT *
FROM Employees
ORDER BY Salary DESC;

Output:

EmployeeID	FirstName	LastName	BirthDate	Salary	City
3	Vijay	Muthu	1990-12-10	82000.00	Madurai
6	Rudra	Kannan	1988-11-05	80000.00	Erode
11	Dhanalakshmi	Gopal	1987-10-21	78000.00	Kanyakumari
1	Karthick AG	Rajan	1980-05-15	75000.00	Chennai
4	Tamil	Selvan	1985-03-30	72000.00	Tiruchirappalli
7	Banumathi	Ramesh	1979-09-25	71000.00	Vellore
5	Naveen	Anand	1992-07-18	69000.00	Salem
9	Rohini	Suresh	1983-04-19	73000.00	Thiruvananthapuram
2	Durai	Kumar	1975-08-22	68000.00	Coimbatore
8	Senthil	Raj	1991-02-14	67000.00	Thanjavur
10	Nila	Prakash	1993-06-07	65000.00	Trichy
12	Riya	Meena	1994-01-12	64000.00	Vellore

Code Explanation: This query selects all columns from the Employees table and orders the results by Salary in descending order.

Example 3: SELECT with GROUP BY and HAVING Clauses

Find the number of employees in each city with salaries above 65,000.

SELECT City, COUNT(*) AS EmployeeCount
FROM Employees
WHERE Salary > 65000
GROUP BY City
HAVING COUNT(*) > 1;

Output:

City	EmployeeCount
Vellore	2

5. Sample Data

To demonstrate the use of the SQL SELECT statement, let's create a sample table named Employees with the following data:

Creating the Employees Table

CREATE TABLE Employees (
    EmployeeID INT PRIMARY KEY,
    FirstName VARCHAR(50),
    LastName VARCHAR(50),
    BirthDate DATE,
    Salary DECIMAL(10, 2),
    City VARCHAR(50)
);

INSERT INTO Employees (EmployeeID, FirstName, LastName, BirthDate, Salary, City) VALUES
(1, 'Karthick AG', 'Rajan', '1980-05-15', 75000.00, 'Chennai'),
(2, 'Durai', 'Kumar', '1975-08-22', 68000.00, 'Coimbatore'),
(3, 'Vijay', 'Muthu', '1990-12-10', 82000.00, 'Madurai'),
(4, 'Tamil', 'Selvan', '1985-03-30', 72000.00, 'Tiruchirappalli'),
(5, 'Naveen', 'Anand', '1992-07-18', 69000.00, 'Salem'),
(6, 'Rudra', 'Kannan', '1988-11-05', 80000.00, 'Erode'),
(7, 'Banumathi', 'Ramesh', '1979-09-25', 71000.00, 'Vellore'),
(8, 'Senthil', 'Raj', '1991-02-14', 67000.00, 'Thanjavur'),
(9, 'Rohini', 'Suresh', '1983-04-19', 73000.00, 'Thiruvananthapuram'),
(10, 'Nila', 'Prakash', '1993-06-07', 65000.00, 'Trichy'),
(11, 'Dhanalakshmi', 'Gopal', '1987-10-21', 78000.00, 'Kanyakumari'),
(12, 'Riya', 'Meena', '1994-01-12', 64000.00, 'Vellore');

Employees Table Data

EmployeeID	FirstName	LastName	BirthDate	Salary	City
1	Karthick AG	Rajan	1980-05-15	75000.00	Chennai
2	Durai	Kumar	1975-08-22	68000.00	Coimbatore
3	Vijay	Muthu	1990-12-10	82000.00	Madurai
4	Tamil	Selvan	1985-03-30	72000.00	Tiruchirappalli
5	Naveen	Anand	1992-07-18	69000.00	Salem
6	Rudra	Kannan	1988-11-05	80000.00	Erode
7	Banumathi	Ramesh	1979-09-25	71000.00	Vellore
8	Senthil	Raj	1991-02-14	67000.00	Thanjavur
9	Rohini	Suresh	1983-04-19	73000.00	Thiruvananthapuram
10	Nila	Prakash	1993-06-07	65000.00	Trichy
11	Dhanalakshmi	Gopal	1987-10-21	78000.00	Kanyakumari
12	Riya	Meena	1994-01-12	64000.00	Vellore

7. Sample Queries

Example 1: SELECT with WHERE Clause

Retrieve the first and last names of employees who earn more than 70,000.

SELECT FirstName, LastName
FROM Employees
WHERE Salary > 70000;

Output:

FirstName	LastName
Karthick AG	Rajan
Vijay	Muthu
Rudra	Kannan
Dhanalakshmi	Gopal

Code Explanation: This query selects the FirstName and LastName of employees whose Salary is greater than 70,000.

Example 2: SELECT with ORDER BY Clause

Retrieve all employee details ordered by their salary in descending order.

SELECT *
FROM Employees
ORDER BY Salary DESC;

Output:

EmployeeID	FirstName	LastName	BirthDate	Salary	City
3	Vijay	Muthu	1990-12-10	82000.00	Madurai
6	Rudra	Kannan	1988-11-05	80000.00	Erode
11	Dhanalakshmi	Gopal	1987-10-21	78000.00	Kanyakumari
1	Karthick AG	Rajan	1980-05-15	75000.00	Chennai
4	Tamil	Selvan	1985-03-30	72000.00	Tiruchirappalli
7	Banumathi	Ramesh	1979-09-25	71000.00	Vellore
5	Naveen	Anand	1992-07-18	69000.00	Salem
9	Rohini	Suresh	1983-04-19	73000.00	Thiruvananthapuram
2	Durai	Kumar	1975-08-22	68000.00	Coimbatore
8	Senthil	Raj	1991-02-14	67000.00	Thanjavur
10	Nila	Prakash	1993-06-07	65000.00	Trichy
12	Riya	Meena	1994-01-12	64000.00	Vellore

Code Explanation: This query selects all columns from the Employees table and orders the results by Salary in descending order.

Example 3: SELECT with GROUP BY and HAVING Clauses

Find the number of employees in each city with salaries above 65,000.

SELECT City, COUNT(*) AS EmployeeCount
FROM Employees
WHERE Salary > 65000
GROUP BY City
HAVING COUNT(*) > 1;

Output:

City	EmployeeCount
Vellore	2

8. Best Practices

Use uppercase for SQL keywords for better readability.
Properly format and indent your SQL code.
Comment your code to explain complex queries.
Specify only the columns you need.
Use aliases to improve readability.
Avoid using SELECT * in production code.

Key Takeaways

The SELECT statement is used to retrieve data from a database.
Selecting specific columns improves performance.
Aliases make query results easier to understand.
Sample data helps in understanding how queries work.
Proper use of clauses like WHERE, ORDER BY, GROUP BY, and HAVING enhance query functionality.

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SQL SELECT Statement

Key Topics

1. Basic SELECT Statement

2. Selecting All Columns

Example: Selecting All Columns

3. Selecting Specific Columns

Example: Selecting Specific Columns

4. Using Aliases

Example: Using Column Aliases

5. Sample Data

Creating the Employees Table

Employees Table Data

6. Sample Queries

Example 1: SELECT with WHERE Clause

Example 2: SELECT with ORDER BY Clause

Example 3: SELECT with GROUP BY and HAVING Clauses

6. Sample Data

Creating the Employees Table

Employees Table Data

7. Sample Queries

Example 1: SELECT with WHERE Clause

Example 2: SELECT with ORDER BY Clause

Example 3: SELECT with GROUP BY and HAVING Clauses

5. Sample Data

Creating the Employees Table

Employees Table Data

7. Sample Queries

Example 1: SELECT with WHERE Clause

Example 2: SELECT with ORDER BY Clause

Example 3: SELECT with GROUP BY and HAVING Clauses

8. Best Practices

Key Takeaways

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