Structured Query Language (SQL) is a Query Language that is used to retrieve, add, update and delete records from a Relational Database Management System (RDBMS). Within SQL there are two main types of statements: Data Definition Language (DDL) and Data Manipulation Language (DML) Statements. This article focuses on Data Manipulation Language (DML). There are four main commands in Data Manipulation Language (DML): SELECT, INSERT, UPDATE and DELETE. These commands can affect one to many rows in a Database.

SQL Data Types

1. String - String Data Types are wrapped in single quotes, i.e. FieldName1 = 'Microsoft'
2. Numerical - Numerical Data Types are only the number, i.e. FieldName1 = 5
3. DateTime - DateTime Data Types are wrapped in single Quotes, i.e. FieldName1 = '2030-01-01'

1. =
2. <>
3. >
4. <
5. >=
6. <=
7. BETWEEN
8. LIKE
9. [NOT] IN
10. IS [NOT] NULL

1. SELECT - The SELECT Statement is used to retrieve rows from a Database Table. The SELECT Statement has the following elements: Field Name(s) and Table Name(s). In addition, a SELECT Statement may also have a Where Clause, an Order By Clause, a Group By Clause and Join Statements. A basic SELECT Statement is in the following form:
SELECT FieldName1, FieldName2, FieldName3 FROM TableName WHERE FieldName1 = Numeric, String or DateTime Value ORDER BY FieldName2 SELECT [ID], [Company], [Last Name], [First Name], [E-mail Address] FROM [Customers] WHERE [ID] = 5 ORDER BY [Last Name], [First Name]

This example is for the Customers Table of Microsoft's Northwind Sample Database.


1. Join Statements - JOIN Statements add related tables to the SQL Statement when the two tables share a field in common.
SELECT TableName1.FieldName1, TableName1.FieldName2, TableName2.FieldName3, TableName2.FieldName4 FROM TableName1 INNER JOIN TableName2 ON TableName1.FieldName1 = TableName2.FieldName3 ORDER BY FieldName2 SELECT [Customers].[ID], [Customers].[Company], [Customers].[Last Name], [Customers].[First Name], [Customers].[E-mail Address], [Orders].[Order ID], [Orders].[Order Date], [Orders].[Shipped Date] FROM [Customers] INNER JOIN [Orders] ON [Customers].[ID] = [Orders].[Customer ID] WHERE [Customers].[ID] = 5

This example is for an Inner Join of the Customers and Orders Table of Microsoft's Northwind Sample Database.

The following is an alternate syntax for the same SQL Statement.

SELECT
TableName1.FieldName1,
TableName1.FieldName2,
TableName2.FieldName3,
TableName2.FieldName4
FROM
TableName1 INNER JOIN TableName2
ON TableName1.FieldName1 = TableName2.FieldName3
WHERE
TableName1.FieldName1 = TableName2.FieldName3


2. INSERT - The INSERT Statement is used to add rows to a Database Table. The INSERT Statement has the following elements: Field Name(s) and a Table Name. An INSERT Statement is in the following form:

INSERT INTO Table_Name (FieldName1, FieldName2, FieldName3) VALUES (FieldValue1, FieldValue2, FieldValue3) INSERT INTO [Customers] ([Company], [Last Name], [First Name], [City]) VALUES ('Software Startup Company', 'Jason', 'Smith', 'San Francisco')

This example is for the Customers Table of Microsoft's Northwind Sample Database.

3. UPDATE - The UPDATE Statement is used to update the values of in one or more rows in a Database Table. The UPDATE Statement has the following elements: Field Name(s) and a Table Name. An UPDATE Statement is in the following form:

UPDATE Table_Name SET FieldName2 = FieldValue2, FieldName3 = FieldValue3, FieldName4 = FieldValue4 WHERE FieldName1 = Numeric, String or DateTime Value UPDATE [Customers] SET [Company] = 'Software Engineering Company', [City] = 'Kansas City' WHERE [ID] = 1

This example is for the Customers Table of Microsoft's Northwind Sample Database. The ID Value is set by the AutoNumber ID field after the record is inserted into the Customers Table.

4. DELETE - The DELETE Statement is used to delete one or more rows in a Database Table. The DELETE Statement has the following elements: a Table Name. A DELETE Statement is in the following form:

DELETE FROM Table_Name WHERE FieldName1 = Numeric, String or DateTime Value DELETE FROM [Customers] WHERE [ID] = 1

This example is for the Customers Table of Microsoft's Northwind Sample Database. The ID Value is set by the AutoNumber ID field after the record is inserted into the Customers Table.