Using Column Aliases to Make Programs Easier to Write
Problem
You’re trying to refer to a column by name from within a program, but the column is calculated from an expression. Consequently, its name is difficult to use.
Solution
Use an alias to give the column a simpler name.
Discussion
Giving Better Names to Query Result Columns shows how column
aliases make query results more meaningful when you’re issuing queries
interactively. Aliases also are useful for programming purposes. If
you’re writing a program that fetches rows into an array and accesses
them by numeric column indexes, the presence or absence of column
aliases makes no difference because aliases don’t change the positions
of columns within the result set. However, aliases make a big
difference if you’re accessing output columns by name because aliases
change those names. You can exploit this fact to give your program
easier names to work with. For example, if your query displays
reformatted message time values from the mail
table using the expression DATE_FORMAT(t,'%M %e, %Y')
, that expression
is also the name you’d have to use when referring to the output
column. That’s not very convenient. If you use AS
date_sent
to give the column an alias, you
can refer to it a lot more easily using the name date_sent
. Here’s an example that shows how
a Perl DBI script might process such values. It retrieves rows into a
hash and refers to column values by name:
$sth = $dbh->prepare ("SELECT srcuser, DATE_FORMAT(t,'%M %e, %Y') AS date_sent ...
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