Retrieving specific information

To retrieve specific information, list the columns containing the information you want. For example:

SELECT columnname,columnname,columnname,... FROM tablename

This query retrieves the values from all the rows for the indicated column(s). For instance, the following query retrieves all the last names and first names stored in the Member table:

SELECT lastName,firstName FROM Member

You can perform mathematical operations on columns when you select them.
For example, you can use the following SELECT query to add two columns:

SELECT col1+col2 FROM tablename

Or you could use the following query:

SELECT price,price*1.08 FROM Pet

The result is the price and the price with the sales tax of 8 percent added.
You can change the name of a column when selecting it, as follows:

SELECT price,price*1.08 AS priceWithTax FROM Pet

The AS clause tells MySQL to give the name priceWithTax to the second column retrieved. Thus, the query retrieves two columns of data: price and priceWithTax.
In some cases, you don’t want to see the values in a column, but you want to know something about the column. For instance, you might want to know the lowest value in the column or the highest value in the column. For example, the query to find out the highest price in the Pet table is

SELECT MAX(price) FROM Pet

SQL words that look like MAX() and SUM(), with parentheses following the name, are functions. Some functions provide information about a column. Other functions change each value selected. For example, SQRT() returns the square root of each value in the column, and DAYNAME() returns the name of the day of the week for each value in a date column, rather than the actual date stored in the column. More than 100 functions are available for use in a SELECT query. For descriptions of all the functions, see the MySQL online manual at dev.mysql.com/doc/refman/5.0/en/functions.html.