We next focus on the use of
aliases. There are two types of
aliases that are used most
frequently: column alias and table
alias.
In short, column aliases exist
to help organizing output. In the
previous example, whenever we see
total sales, it is listed as SUM(sales).
While this is comprehensible, we
can envision cases where the
column heading can be complicated
(especially if it involves several
arithmetic operations). Using a
column alias would greatly make
the output much more readable.
The second type of alias is the
table alias. This is accomplished
by putting an alias directly after
the table name in the FROM clause.
This is convenient when you want
to obtain information from two
separate tables (the technical
term is 'perform joins'). The
advantage of using a table alias
when doing joins is readily
apparent when we talk about joins.
Before we get into joins,
though, let's look at the syntax
for both the column and table
aliases:
SELECT
"table_alias"."column_name1"
"column_alias"
FROM "table_name"
"table_alias"
Briefly, both types of aliases
are placed directly after the item
they alias for, separate by a
white space. We again use our
table, Store_Information,
Table Store_Information
| store_name |
Sales |
Date |
| Los Angeles |
$1500 |
Jan-05-1999 |
| San Diego |
$250 |
Jan-07-1999 |
| Los Angeles |
$300 |
Jan-08-1999 |
| Boston |
$700 |
Jan-08-1999 |
We use the same example as that in
the SQL
GROUP BY section,
except that we have put in both
the column alias and the table
alias:
SELECT
A1.store_name Store, SUM(A1.Sales)
"Total Sales"
FROM Store_Information A1
GROUP BY A1.store_name
Result:
Store Total
Sales
Los Angeles $1800
San Diego $250
Boston $700
