Reading rows
Until now, we have basically learned how to insert, modify, or delete rows. We also used queries such as the following one to verify what we've written into the tables:
SELECT * FROM <table_name>;
This is the simplest query we could write: it simply reads all the columns and rows from a table. However, normally we only need to read a subset of columns and rows. We may also need to request some additional operations on the data we extract, such as ordering or grouping. The SELECT statement is the most complex, and we will fully explore it in this section.
Specifying the table and column names
The basic syntax for SELECT is:
SELECT <expression_list> FROM <table_name>;
Until now, we have always used a n asterisk (*) as an expression list. This character means all columns. However, generally, we only need to read a subset of columns. Simply typing a single character is easier, but it will cause our database to read unnecessary data and send it to the clients. To...