1 - Basic SQL Query statements

Reference: https://www.w3schools.com/sql/sql_select.asp

Customers

Categories

Employees

Orders

Products

OrderDetails

Shippers

Suppliers

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The SELECT statement is used to select data from a database.

The result is stored in a result table, called the result-set.

SELECT column_name,column_name FROM table_name;

ex:SELECT CustomerName,City FROM Customers;

SELECT * FROM table_name;

ex:SELECT * FROM Customers;

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The DISTINCT keyword can be used to return only distinct (different) values.

SELECT DISTINCT column_name,column_name FROM table_name;

ex:SELECT DISTINCT City FROM Customers;

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WHERE

SELECT column_name,column_name FROM table_name
WHERE column_name operator value;

ex1: SELECT * FROM Customers WHERE Country='Mexico';

ex2: SELECT * FROM Customers WHERE CustomerID=1;

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LIMIT

SELECT column_name,column_name FROM table_name
LIMIT 5; // select first 5 rows(MYSQL). varies for different DBS.. some use SELECT TOP instead(Oracle)

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AND OR Operators

ex1: SELECT * FROM Customers WHERE Country='Germany' AND City='Berlin';

ex2: SELECT * FROM Customers WHERE City='München' OR City='Berlin';

ex3: SELECT * FROM Customers WHERE Country='Germany' AND 

                                        (City='München' OR City='Berlin');

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ORDER BY  --- ASC/DESC

SELECT column_name, column_name FROM table_name

ORDER BY column_name ASC|DESC, column_name ASC|DESC;

ex: SELECT * FROM Customers ORDER BY  Country ASC, CustomerName DESC;

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INSERT INTO  --- VALUES

INSERT INTO Customers (CustomerName, ContactName, Address, City, PostalCode, Country)
VALUES ('Cardinal','Tom B. Erichsen','Skagen 21','Stavanger','4006','Norway');

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UPDATE <<tablename>> SET <<column-name>> = value WHERE (condition);

ex: UPDATE Customers SET ContactName='Alfred Schmidt', City='Frankfurt'

WHERE CustomerID=1;

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DELETE FROM table_name WHERE (condition);

or

DELETE * FROM table_name;//deletes all records

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