SQL Class Note By Amit Maity PowerPoint Presentation

SQL cheat sheet
Comprehensive
Data Manipulation Language (DML) Commands
Command Description Syntax Example
SELECT The SELECT command retrieves
data from a database.
SELECT column1, column2 FROM
table_name;
SELECT first_name, last_name
FROM customers;
INSERT The INSERT command adds new
records to a table.
INSERT INTO table_name
(column1, column2) VALUES
(value1, value2);
INSERT INTO customers
(first_name, last_name)
VALUES ('Mary', 'Doe');
UPDATE The UPDATE command is used
to modify existing records in a
table.
UPDATE table_name SET column1
= value1, column2 = value2
WHERE condition;
UPDATE employees SET
employee_name = ‘John Doe’,
department = ‘Marketing’;
DELETE The DELETE command removes
records from a table.
DELETE FROM table_name WHERE
condition;
DELETE FROM employees WHERE
employee_name = ‘John Doe’;
Data Definition Language (DDL) Commands
CREATE The CREATE command creates a
new database and objects, such
as a table, index, view, or stored
procedure.
CREATE TABLE table_name
(column1 datatype1,
column2 datatype2, …);
CREATE TABLE employees (
employee_id INT
PRIMARY KEY,
first_name
VARCHAR(50),
last_name
VARCHAR(50),
age INT
);
ALTER The ALTER command adds,
deletes, or modifies columns in
an existing table.
ALTER TABLE table_name
ADD column_name datatype;
ALTER TABLE customers ADD
email VARCHAR(100);
DROP The DROP command is used to
drop an existing table in a database.
DROP TABLE table_name; DROP TABLE customers;
TRUNCATE The TRUNCATE command is
used to delete the data inside a
table, but not the table itself.
TRUNCATE TABLE
table_name;
TRUNCATE TABLE customers;

Data Control Language (DCL) Commands
GRANT The GRANT command is used to
give specific privileges to users
or roles.
GRANT SELECT, INSERT ON
table_name TO user_name;
GRANT SELECT, INSERT ON
employees TO ‘John Doe’;
REVOKE The REVOKE command is used
to take away privileges
previously granted to users or
roles.
REVOKE SELECT, INSERT ON
table_name FROM
user_name;
REVOKE SELECT, INSERT ON
employees FROM ‘John
Doe’;
Querying Data Commands
SELECT Statement The SELECT statement is the
primary command used to
retrieve data from a database
SELECT column1, column2
FROM table_name;
SELECT first_name,
last_name FROM customers;
WHERE Clause The WHERE clause is used to
filter rows based on a specified
condition.
SELECT * FROM table_name
WHERE condition;
SELECT * FROM customers
WHERE age > 30;
ORDER BY Clause The ORDER BY clause is used to
sort the result set in ascending
or descending order based on a
specified column.
SELECT * FROM table_name
ORDER BY column_name
ASC|DESC;
SELECT * FROM products
ORDER BY price DESC;
GROUP BY Clause The GROUP BY clause groups
rows based on the values in a
specified column. It is often
used with aggregate functions
like COUNT, SUM, AVG, etc.
SELECT column_name,
COUNT(*) FROM table_name
GROUP BY column_name;
SELECT category, COUNT(*)
FROM products GROUP BY
category;
HAVING Clause The HAVING clause filters
grouped results based on a
specified condition.
SELECT column_name,
COUNT(*) FROM table_name
GROUP BY column_name
HAVING condition;
SELECT category, COUNT(*)
FROM products GROUP BY
category HAVING COUNT(*)
> 5;

Joining Commands
INNER JOIN The INNER JOIN command
returns rows with matching
values in both tables.
SELECT * FROM table1
INNER JOIN table2 ON
table1.column =
table2.column;
SELECT * FROM employees
INNER JOIN departments ON
employees.department_id =
departments.id;
LEFT JOIN/LEFT OUTER JOIN The LEFT JOIN command
returns all rows from the left
table (first table) and the
matching rows from the right
table (second table).
SELECT * FROM table1 LEFT
JOIN table2 ON
table1.column =
table2.column;
SELECT * FROM employees LEFT
JOIN departments ON
employees.department_id =
departments.id;
RIGHT JOIN/RIGHT OUTER
JOIN
The RIGHT JOIN command
returns all rows from the right
table (second table) and the
matching rows from the left
table (first table).
RIGHT JOIN table2 ON
table1.column =
table2.column;
SELECT *
FROM employees
RIGHT JOIN departments
ON employees.department_id =
departments.department_id;
FULL JOIN/FULL OUTER JOIN The FULL JOIN command
returns all rows when there is a
match in either the left table or
the right table.
SELECT * FROM table1 FULL
JOIN table2 ON
table1.column =
table2.column;
SELECT *
FROM employees
LEFT JOIN departments ON
employees.employee_id =
departments.employee_id
UNION
SELECT *
FROM employees
RIGHT JOIN departments ON
employees.employee_id =
departments.employee_id;
CROSS JOIN The CROSS JOIN command
combines every row from the
first table with every row from
the second table, creating a
Cartesian product.
CROSS JOIN table2;
CROSS JOIN departments;
SELF JOIN The SELF JOIN command joins
a table with itself.
SELECT * FROM table1 t1,
table1 t2 WHERE t1.column
= t2.column;
SELECT * FROM employees t1,
employees t2
WHERE t1.employee_id =
t2.employee_id;
NATURAL JOIN The NATURAL JOIN command
matches columns with the
same name in both tables.
NATURAL JOIN table2;
NATURAL JOIN departments;

Subqueries in SQL
IN The IN command is used to
determine whether a value
matches any value in a subquery
result. It is often used in the
WHERE clause.
SELECT column(s) FROM
table WHERE value IN
(subquery);
SELECT * FROM customers
WHERE city IN (SELECT
city FROM suppliers);
ANY The ANY command is used to
compare a value to any value
returned by a subquery. It can
be used with comparison
operators like =, >, <, etc.
table WHERE value < ANY
(subquery);
SELECT * FROM products
WHERE price < ANY (SELECT
unit_price FROM
supplier_products);
ALL The ALL command is used to
compare a value to all values
returned by a subquery. It can
be used with comparison
operators like =, >, <, etc.
table WHERE value > ALL
(subquery);
SELECT * FROM orders
WHERE order_amount > ALL
(SELECT total_amount FROM
previous_orders);
Aggregate Functions Commands
COUNT() The COUNT command counts
the number of rows or non-null
values in a specified column.
SELECT COUNT(column_name)
FROM table_name;
SELECT COUNT(age) FROM
employees;
SUM() The SUM command is used to
calculate the sum of all values in
a specified column.
SELECT SUM(column_name)
FROM table_name;
SELECT SUM(revenue) FROM
sales;
AVG() The AVG command is used to
calculate the average (mean) of
all values in a specified column.
SELECT AVG(column_name)
FROM table_name;
SELECT AVG(price) FROM
products;
MIN() The MIN command returns the
minimum (lowest) value in a
specified column.
SELECT MIN(column_name)
FROM table_name;
SELECT MIN(price) FROM
products;
MAX() The MAX command returns the
maximum (highest) value in a
specified column.
SELECT MAX(column_name)
FROM table_name;
SELECT MAX(price) FROM
products;

String Functions in SQL
CONCAT() The CONCAT command
concatenates two or more
strings into a single string.
SELECT CONCAT(string1,
string2, …) AS
concatenated_string FROM
table_name;
SELECT CONCAT(first_name,
' ', last_name) AS
full_name FROM employees;
SUBSTRING()/SUBSTR() The SUBSTRING command
extracts a substring from a
string.
SELECT SUBSTRING(string
FROM start_position [FOR
length]) AS substring
FROM table_name;
SELECT
SUBSTRING(product_name
FROM 1 FOR 5) AS
substring FROM products;
CHAR_LENGTH()/LENGTH() The LENGTH command returns
the length (number of
characters) of a string.
SELECT
CHAR_LENGTH(string) AS
length FROM table_name;
SELECT
CHAR_LENGTH(product_name)
AS length FROM products;
UPPER() The UPPER command converts
all characters in a string to
uppercase.
SELECT UPPER(string) AS
uppercase_string FROM
table_name;
SELECT UPPER(first_name)
AS uppercase_first_name
FROM employees;
LOWER() The LOWER command converts
all characters in a string to
lowercase.
SELECT LOWER(string) AS
lowercase_string FROM
table_name;
SELECT LOWER(last_name)
AS lowercase_last_name
FROM employees;
TRIM() The TRIM command removes
specified prefixes or suffixes (or
whitespace by default) from a
string.
SELECT TRIM([LEADING |
TRAILING | BOTH]
characters FROM string)
AS trimmed_string FROM
table_name;
SELECT TRIM(TRAILING ' '
FROM full_name) AS
trimmed_full_name FROM
customers;
LEFT() The LEFT command returns a
specified number of characters
from the left of a string.
SELECT LEFT(string,
num_characters) AS
left_string FROM
table_name;
SELECT
LEFT(product_name, 5)
AS left_product_name
FROM products;
RIGHT() The RIGHT command returns a
specified number of characters
from the right of a string.
SELECT RIGHT(string,
num_characters) AS
right_string FROM
table_name;
SELECT
RIGHT(order_number, 4) AS
right_order_number FROM
orders;
REPLACE() The REPLACE command
replaces occurrences of a
substring within a string.
SELECT REPLACE(string,
old_substring,
new_substring) AS
replaced_string FROM
table_name;
SELECT
REPLACE(description,
'old_string',
'new_string') AS
replaced_description FROM
product_descriptions;

Date and Time SQL Commands
CURRENT_DATE() The CURRENT_DATE command
returns the current date.
SELECT CURRENT_DATE() AS
current_date;
CURRENT_TIME() The CURRENT_TIME command
returns the current time.
SELECT CURRENT_TIME() AS
current_time;
CURRENT_TIMESTAMP() The CURRENT_TIMESTAMP
command returns the current
date and time.
SELECT
CURRENT_TIMESTAMP() AS
current_timestamp;
DATE_PART() The DATE_PART command
extracts a specific part (e.g.,
year, month, day) from a date or
time.
SELECT DATE_PART('part',
date_expression) AS
extracted_part;
DATE_ADD()/DATE_SUB() The DATE_ADD command adds
or subtracts a specified number
of days, months, or years
to/from a date.
SELECT
DATE_ADD(date_expression,
INTERVAL value unit) AS
new_date;
EXTRACT() The EXTRACT command
extracts a specific part (e.g.,
year, month, day) from a date or
time.
SELECT EXTRACT(part FROM
date_expression) AS
extracted_part;
TO_CHAR() The TO_CHAR command
converts a date or time to a
specified format.
SELECT
TO_CHAR(date_expression,
'format') AS
formatted_date;
TIMESTAMPDIFF() The TIMESTAMPDIFF command
calculates the difference
between two timestamps in a
specified unit (e.g., days, hours,
minutes).
SELECT
TIMESTAMPDIFF(unit,
timestamp1, timestamp2)
AS difference;
DATEDIFF() The DATEDIFF command
calculates the difference in days
between two dates.
SELECT DATEDIFF(date1,
date2) AS
difference_in_days;

Conditional Expressions
CASE Statement The CASE statement allows you
to perform conditional logic
within a query.
SELECT
column1,
column2,
CASE
WHEN condition1
THEN result1
WHEN condition2
THEN result2
ELSE
default_result
END AS alias
FROM table_name;
SELECT
order_id,
total_amount,
CASE
WHEN total_amount
> 1000 THEN 'High Value
Order'
WHEN total_amount
> 500 THEN 'Medium Value
Order'
ELSE 'Low Value
Order'
END AS order_status
FROM orders;
IF() Function The IF() function evaluates a
condition and returns a value
based on the evaluation.
SELECT IF(condition,
true_value, false_value)
AS alias FROM table_name;
SELECT
name,
age,
IF(age > 50,
'Senior', 'Junior') AS
employee_category
FROM employees;
COALESCE() Function The COALESCE() function
returns the first non-null value
from a list of values.
SELECT COALESCE(value1,
value2, …) AS alias
FROM table_name;
SELECT
COALESCE(first_name,
middle_name) AS
preferred_name
FROM employees;
NULLIF() Function The NULLIF() function returns
null if two specified expressions
are equal.
SELECT
NULLIF(expression1,
expression2) AS alias
FROM table_name;
SELECT
NULLIF(total_amount,
discounted_amount) AS
diff_amount FROM orders;

Set Operations
UNION The UNION operator combines
the result sets of two or more
SELECT statements into a single
result set.
FROM table1
UNION
FROM table2;
SELECT first_name,
last_name FROM customers
UNION
SELECT first_name,
last_name FROM employees;
INTERSECT The INTERSECT operator returns
the common rows that appear in
both result sets.
FROM table1
INTERSECT
FROM table2;
SELECT first_name,
INTERSECT
SELECT first_name,
EXCEPT The EXCEPT operator returns
the distinct rows from the left
result set that are not present in
the right result set.
FROM table1
EXCEPT
FROM table2;
SELECT first_name,
EXCEPT
SELECT first_name,
Transaction Control Commands
COMMIT The COMMIT command is used
to save all the changes made
during the current transaction
and make them permanent.
COMMIT; BEGIN TRANSACTION;
= SqL statements and
changes within the
transaction
INSERT INTO employees
(name, age) VALUES
('Alice', 30);
UPDATE products SET price
= 25.00 WHERE category =
'Electronics';
COMMIT;
ROLLBACK The ROLLBACK command is
used to undo all the changes
made during the current
transaction and discard them.
ROLLBACK; BEGIN TRANSACTION;
changes within the
transaction

(name, age) VALUES
('Bob', 35);
'Electronics';
ROLLBACK;
SAVEPOINT The SAVEPOINT command is
used to set a point within a
transaction to which you can
later roll back.
SAVEPOINT savepoint_name; BEGIN TRANSACTION;
(name, age) VALUES
('Carol', 28);
SAVEPOINT before_update;
'Electronics';
SAVEPOINT after_update;
DELETE FROM customers
WHERE age > 60;
ROLLBACK TO
before_update;
= At this point, the
DELETE is rolled back,
but the UPDATE remains.
COMMIT;
ROLLBACK TO SAVEPOINT The ROLLBACK TO SAVEPOINT
command is used to roll back to
a specific savepoint within a
transaction.
ROLLBACK TO SAVEPOINT
savepoint_name;
BEGIN TRANSACTION;
(name, age) VALUES
('David', 42);
SAVEPOINT before_update;
'Electronics';
SAVEPOINT after_update;
DELETE FROM customers
WHERE age > 60;
= Rollback to the
savepoint before the
update
ROLLBACK TO SAVEPOINT
before_update;
= At this point, the
UPDATE is rolled back,
but the INSERT remains.

COMMIT;
SET TRANSACTION The SET TRANSACTION
command is used to configure
properties for the current
transaction, such as isolation
level and transaction mode.
SET TRANSACTION
[ISOLATION LEVEL { READ
COMMITTED | SERIALIZABLE
}]
BEGIN TRANSACTION;
= Set the isolation
level to READ COMMITTED
SET TRANSACTION ISOLATION
LEVEL READ COMMITTED;
changes within the
transaction
(name, age) VALUES
('Emily', 35);
'Electronics';
COMMIT;

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