As we mentioned earlier, SQL resembles a human language more than a computer language because it has a simple, defined imperative structure. Much like an English sentence, individual SQL commands, called “queries,” can be broken down into language parts. Consider the following examples:

CREATE   TABLE             people (name CHAR(10))
verb     object            adjective phrase

INSERT   INTO people       VALUES ('me')
verb     indirect object   direct object

SELECT   name              FROM people             WHERE name LIKE '%e'
verb     direct object     indirect object         adjective phrase

Most implementations of SQL, including MySQL, are case insensitive. Specifically, it does not matter how you type SQL keywords as long as the spelling is correct. The previous CREATE example could just as well be:

cREatE TAblE people (name cHaR(10))

The case insensitivity extends only to SQL keywords.^[1] In MySQL, names of databases, tables, and columns are case-sensitive. This case sensitivity is not necessarily true for all database engines. Thus, if you are writing an application that should work against all databases, you should assume that names are case sensitive.

This first element of an SQL query is always a verb. The verb expresses the action you wish the database engine to take. While the rest of the statement varies from verb to verb, they all follow the same general format: you name the object upon which you are acting and then describe the data you are using for the action. For example, the query CREATE TABLE people (name CHAR(10)) uses the verb CREATE, followed by the object TABLE. The rest of the query describes the table to be created.

An SQL query originates with a client (the application that provides the façade through which a user interacts with the database). The client constructs a query based on user actions and sends the query to the SQL server. The server must then process the query and perform the specified action. Once the server has done its job, it returns some value or set of values to the client.

Because the primary focus of SQL is to communicate actions to the database server, it does not have the flexibility of a general-purpose language. Most of the functionality of SQL concerns input to and output from the database: adding, changing, deleting, and reading data. SQL provides other functionality, but always with an eye towards how it can be used to manipulate the data within the database.