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A database most often contains one or more tables. Each table is identified by a name (e.g. "Customers" or "Orders"). Tables contain records (rows) with data
A database most often contains one or more tables. Each table is identified by a name (e.g. "Customers" or "Orders"). Tables contain records (rows) with data.
In this tutorial we will use the well-known Northwind sample database (included in MS Access and MS SQL Server).
Below is a selection from the "Customers" table:
CustomerID | CustomerName | ContactName | Address | City | PostalCode | Country |
---|---|---|---|---|---|---|
1 |
Alfreds Futterkiste | Maria Anders | Obere Str. 57 | Berlin | 12209 | Germany |
2 | Ana Trujillo Emparedados y helados | Ana Trujillo | Avda. de la Constitución 2222 | México D.F. | 05021 | Mexico |
3 | Antonio Moreno Taquería | Antonio Moreno | Mataderos 2312 | México D.F. | 05023 | Mexico |
4 |
Around the Horn | Thomas Hardy | 120 Hanover Sq. | London | WA1 1DP | UK |
5 | Berglunds snabbköp | Christina Berglund | Berguvsvägen 8 | Luleå | S-958 22 | Sweden |
The table above contains five records (one for each customer) and seven columns (CustomerID, CustomerName, ContactName, Address, City, PostalCode, and Country).
Most of the actions you need to perform on a database are done with SQL statements.
The following SQL statement selects all the records in the "Customers" table:
SELECT * FROM Customers;
In this tutorial we will teach you all about the different SQL statements.
select
is the same as
SELECT
In this tutorial we will write all SQL keywords in upper-case.
Some database systems require a semicolon at the end of each SQL statement.
Semicolon is the standard way to separate each SQL statement in database systems that allow more than one SQL statement to be executed in the same call to the server.
In this tutorial, we will use semicolon at the end of each SQL statement.
SELECT
- extracts data from a databaseUPDATE
- updates data in a databaseDELETE
- deletes data from a databaseINSERT INTO
- inserts new data into a databaseCREATE DATABASE
- creates a new databaseALTER DATABASE
- modifies a databaseCREATE TABLE
- creates a new tableALTER TABLE
- modifies a tableDROP TABLE
- deletes a tableCREATE INDEX
- creates an index (search key)DROP INDEX
- deletes an index