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MySQL Cookbook
book

MySQL Cookbook

by Paul DuBois
October 2002
Intermediate to advanced content levelIntermediate to advanced
1024 pages
27h 26m
English
O'Reilly Media, Inc.
Content preview from MySQL Cookbook

Sorting in User-Defined Orders

Problem

You want to define the sort order for all values in a column.

Solution

Use FIELD( ) to map column values onto a sequence that places the values in the desired order.

Discussion

The previous section showed how to make a specific group of rows go to the head of the sort order. If you want to impose a specific order on all values in a column, use the FIELD( ) function to map them to a list of numeric values and use the numbers for sorting. FIELD( ) compares its first argument to the following arguments and returns a number indicating which one of them it matches. The following FIELD( ) call compares value to str1, str2, str3, and str4, and returns 1, 2, 3, or 4, depending on which one of them value is equal to:

FIELD(value,str1,str2,str3,str4)

The number of comparison values need not be four; FIELD( ) takes a variable-length argument list. If value is NULL or none of the values match, FIELD( ) returns 0.

FIELD( ) can be used to sort an arbitrary set of values into any order you please. For example, to display driver_log records for Henry, Suzi, and Ben, in that order, do this:

mysql> SELECT * FROM driver_log
    -> ORDER BY FIELD(name,'Henry','Suzi','Ben'); +--------+-------+------------+-------+ | rec_id | name | trav_date | miles | +--------+-------+------------+-------+ | 3 | Henry | 2001-11-29 | 300 | | 4 | Henry | 2001-11-27 | 96 | | 6 | Henry | 2001-11-26 | 115 | | 8 | Henry | 2001-12-01 | 197 | | 10 | Henry | 2001-11-30 | 203 | | 2 | Suzi | 2001-11-29 ...
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Publisher Resources

ISBN: 0596001452Catalog PageErrata