SQL Structure and Syntax

You'll find SQL simple to learn and use if you know the proper syntax for passing data. For the most part, SQL consists of keywords individual words with a predefined meaning. Most keywords can include arguments, just like functions and procedures. A keyword with arguments is known as a clause.

Combined clauses that make a request of the database engine are called statements. A statement can consist of just one clause, but usually, there is more than one.

The most basic and general statement form is the following:

 action fieldlist FROM datasource 

where action is one of many keywords that defines the statement's purpose, fieldlist defines the fields to act upon, and datasource identifies the table in which the data is stored.

You can limit the records acted upon by adding a WHERE clause in the form

 action fieldlist FROM datasource [WHERE condition] 

Table A.1 lists the most common action SQL keywords. Table A.2 lists several SQL keywords that act as predicates that supply more information to the statement.

Table A.1. Common SQL action Keywords

Keyword	Purpose	Syntax
SELECT	Retrieve data	SELECT fieldlist FROM datasource
UPDATE SET	Modify data	UPDATE datasource SET col = expression
DELETE	Delete records	DELETE FROM datasource
INSERT INTO	Insert (or append) records into any existing table	INSERT INTO target SELECT datasource
SELECT INTO	Copy an existing table's structure and data to a new table	SELECT fieldlist INTO newtable FROM datasource

Table A.2. Additional Information Keywords and Predicates

Keyword	Purpose	Syntax
ALL	Predicate that retrieves or acts upon all the rows in the data source	SELECT ALL FROM datasource
DISTINCT	Predicate that returns unique values in specified fields	SELECT DISTINCT fieldlist FROM datasource
DISTINCTROW	Predicate that returns unique records	SELECT DISTINCTROW fieldlist FROM datasource
FROM	Identifies the data source	FROM datasource
TOP	Limits the number of records retrieved or acted upon	TOP number
WHERE	Condition expression that conditionally limits records	WHERE conditionalexpression
GROUP BY	Arranges records by similar values	GROUP BY fieldlist
ORDER BY	Sorts records by a field or fields	ORDER BY fieldlist
HAVING	Determines which records make it to a group	HAVING condition