Categorizing Non-Categorical Data : COUNT « Aggregate Functions « SQL / MySQL






  1. SQL / MySQL
  2. Aggregate Functions
  3. COUNT

Categorizing Non-Categorical Data

       
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 COUNT(pop), COUNT(DISTINCT pop) FROM states;
+------------+---------------------+
| COUNT(pop) | COUNT(DISTINCT pop) |
+------------+---------------------+
|         23 |                  23 |
+------------+---------------------+
1 row in set (0.00 sec)

mysql>
mysql> drop table states;
Query OK, 0 rows affected (0.00 sec)








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14.Count number of rows containing duplicated names
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16.Eliminating Duplicates from a Query Result
17.Removing Duplicates of a Particular Row
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19.How many days did Suzi drive?
20.How many messages were sent by each message sender
21.How many states did the United States consist of at the beginning of the 20th century?
22.Or to count weekend versus weekday trips
23.Count each value and see which one is most common
24.Generating Frequency Distributions
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26.Counting Missing Values
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