Simple Queries
The simplest SQL
query is to ask for certain columns in
all rows of a table. The SELECT syntax for this
form of query can be expressed as simply as:
SELECT column, column, ..., column FROM table
or:
SELECT * FROM table
which will query and fetch back all the columns within the specified table.
Therefore, to select some of the rows from some columns in the
megaliths table, the following SQL statement can
be used:
SELECT name, location, mapref FROM megaliths
which would return the following information:
+---------------------------------------------------------------+ | name | location | mapref | +---------------------------------------------------------------+ | Callanish I | Callanish, Isle of Lewis | NB 213 330 | | Lundin Links | Lundin Links, Fife, Scotland | NO 404 027 | | Stonehenge | Near Amesbury, Wiltshire, England | SU 123 400 | | Avebury | Avebury, Wiltshire, England | SU 103 700 | | Sunhoney | Near Insch, Aberdeenshire | NJ 716 058 | +---------------------------------------------------------------+
So even with the simplest SQL imaginable, the inherent flexibility of the syntax allows us to easily specify exactly which information we want from the database without having to write lots of excruciating lines of code to get it.
Another aspect of the relational database methodology is now visible, in that even though the database contains information on all the columns within a particular table, only a subset of the available columns needs to be retrieved. Therefore, ...