- Sorting Data
- Sorting by Multiple Columns
- Sorting by Column Position
- Specifying Sort Direction
- Summary
This chapter is from the book
This chapter is from the book
This chapter is from the book
Specifying Sort Direction
Data sorting is not limited to ascending sort orders (from A to Z). Although this is the default sort order, the ORDER BY clause can also be used to sort in descending order (from Z to A). To sort by descending order, the keyword DESC must be specified.
The following example sorts the products by price in descending order (most expensive first):
INPUT
SELECT prod_id, prod_price, prod_name FROM Products ORDER BY prod_price DESC;
OUTPUT
prod_id prod_price prod_name ------- ---------- -------------------- BR03 11.9900 18 inch teddy bear RYL01 9.4900 King doll RYL02 9.4900 Queen doll BR02 8.9900 12 inch teddy bear BR01 5.9900 8 inch teddy bear RGAN01 4.9900 Raggedy Ann BNBG01 3.4900 Fish bean bag toy BNBG02 3.4900 Bird bean bag toy BNBG03 3.4900 Rabbit bean bag toy
But what if you were to sort by multiple columns? The following example sorts the products in descending order (most expensive first), plus product name:
INPUT
SELECT prod_id, prod_price, prod_name FROM Products ORDER BY prod_price DESC, prod_name;
OUTPUT
prod_id prod_price prod_name ------- ---------- -------------------- BR03 11.9900 18 inch teddy bear RYL01 9.4900 King doll RYL02 9.4900 Queen doll BR02 8.9900 12 inch teddy bear BR01 5.9900 8 inch teddy bear RGAN01 4.9900 Raggedy Ann BNBG02 3.4900 Bird bean bag toy BNBG01 3.4900 Fish bean bag toy BNBG03 3.4900 Rabbit bean bag toy
ANALYSIS
The DESC keyword only applies to the column name that directly precedes it. In the example above, DESC was specified for the prod_price column, but not for the prod_name column. Therefore, the prod_price column is sorted in descending order, but the prod_name column (within each price) is still sorted in standard ascending order.
TIP
Sorting Descending on Multiple Columns If you want to sort descending on multiple columns, be sure each column has its own DESC keyword.
It is worth noting that DESC is short for DESCENDING, and both keywords may be used. The opposite of DESC is ASC (or ASCENDING), which may be specified to sort in ascending order. In practice, however, ASC is not usually used because ascending order is the default sequence (and is assumed if neither ASC nor DESC are specified).
TIP
Case Sensitivity and Sort Orders When you are sorting textual data, is A the same as a? And does a come before B or after Z? These are not theoretical questions, and the answers depend on how the database is set up.
In dictionary sort order, A is treated the same as a, and that is the default behavior for most Database Management Systems. However, most good DBMSs enable database administrators to change this behavior if needed. (If your database contains lots of foreign language characters, this might become necessary.)
The key here is that if you do need an alternate sort order, you cannot accomplish it with a simple ORDER BY clause. You must contact your database administrator.