Mega Code Archive
Eliminating Duplicates from a Self-Join Result
<![CDATA[
mysql>
mysql> CREATE TABLE states
-> (
-> name VARCHAR(30) NOT NULL, # state name
-> abbrev CHAR(2) NOT NULL, # 2-char abbreviation
-> statehood DATE, # date of entry into the Union
-> pop BIGINT, # population as of 4/1990
-> PRIMARY KEY (abbrev)
-> );
Query OK, 0 rows affected (0.00 sec)
mysql>
mysql> insert into states(name, abbrev, statehood, pop)values
-> ("Alabama","AL","1819-12-14",4040587),
-> ("Alaska","AK","1959-01-03",550043),
-> ("Arizona","AZ","1912-02-14",3665228),
-> ("Arkansas","AR","1836-6-15",2350725),
-> ("California","CA","1850-9-9",29760021),
-> ("Colorado","CO","1876-8-1",3294394),
-> ("Connecticut","CT","1788-1-9",3287116),
-> ("Delaware","DE","1787-12-7",666168),
-> ("Florida","FL","1845-3-3",12937926),
-> ("Georgia","GA","1788-1-2",6478216),
-> ("Hawaii","HI","1959-08-21",1108229),
-> ("Idaho","ID","1890-7-3",1006749),
-> ("Illinois","IL","1818-12-3",11430602),
-> ("Indiana","IN","1816-12-11",5544159),
-> ("Iowa","IA","1846-12-28",2776755),
-> ("Kansas","KS","1861-1-29",2477574),
-> ("Kentucky","KY","1792-6-1",3685296),
-> ("Louisiana","LA","1812-4-30",4219973),
-> ("Maine","ME","1820-3-15",1227928),
-> ("Maryland","MD","1788-4-28",4781468),
-> ("Massachusetts","MA","1788-2-6",6016425),
-> ("Michigan","MI","1837-1-26",9295297),
-> ("Minnesota","MN","1858-5-11",4375099);
Query OK, 23 rows affected (0.00 sec)
Records: 23 Duplicates: 0 Warnings: 0
mysql>
mysql>
mysql> SELECT YEAR(s2.statehood) AS year, s1.name, s2.name
-> FROM states AS s1, states AS s2
-> WHERE YEAR(s1.statehood) = YEAR(s2.statehood)
-> AND s1.name != s2.name
-> ORDER BY year, s1.name, s2.name;
+------+---------------+---------------+
| year | name | name |
+------+---------------+---------------+
| 1788 | Connecticut | Georgia |
| 1788 | Connecticut | Maryland |
| 1788 | Connecticut | Massachusetts |
| 1788 | Georgia | Connecticut |
| 1788 | Georgia | Maryland |
| 1788 | Georgia | Massachusetts |
| 1788 | Maryland | Connecticut |
| 1788 | Maryland | Georgia |
| 1788 | Maryland | Massachusetts |
| 1788 | Massachusetts | Connecticut |
| 1788 | Massachusetts | Georgia |
| 1788 | Massachusetts | Maryland |
| 1959 | Alaska | Hawaii |
| 1959 | Hawaii | Alaska |
+------+---------------+---------------+
14 rows in set (0.00 sec)
mysql>
mysql> drop table states;
Query OK, 0 rows affected (0.00 sec)
mysql>
]]>