Database

In a relational database, data is stored in tables. An example table would relate Social Security Number, Name, and Address:

Now, let's say you want to see the address of each employee. Use the SELECT statement, like so:

SELECT FirstName, LastName, Address, City, State
FROM EmployeeAddressTable;

The following is the results of your query of the database:

To explain what you just did, you asked for the all of data in the EmployeeAddressTable, and specifically, you asked for the columns called FirstName, LastName, Address, City, and State. Note that column names and table names do not have spaces...they must be typed as one word; and that the statement ends with a semicolon (;). The general form for a SELECT statement, retrieving all of the rows in the table is:

SELECT ColumnName, ColumnName, ... 
				FROM TableName; 
				

To get all columns of a table without typing all column names, use:

SELECT *
				FROM TableName;
				

Each database management system (DBMS) and database software has different methods for logging in to the database and entering SQL commands; see the local computer "guru" to help you get onto the system, so that you can use SQL.

Conditional Selection

To further discuss the SELECT statement, let's look at a new example table (for hypothetical purposes only):

There are six logical operators in SQL, and after introducing them, we'll see how they're used:

The WHERE clause is used to specify that only certain rows of the table are displayed, based on the criteria described in that WHERE clause. It is most easily understood by looking at a couple of examples.