Use a two-stage approach involving one query that selects the maximum size into a SQL variable, and another th : Variable « Select Clause « SQL / MySQL






  1. SQL / MySQL
  2. Select Clause
  3. Variable

Use a two-stage approach involving one query that selects the maximum size into a SQL variable, and another th

       
at refers to the variable in its WHERE clause
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 (0.01 sec)

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> SELECT @max := MAX(pop) FROM states;
+------------------+
| @max := MAX(pop) |
+------------------+
|         29760021 |
+------------------+
1 row in set (0.00 sec)

mysql> SELECT @max AS 'highest population', name FROM states WHERE pop = @max;
+--------------------+------------+
| highest population | name       |
+--------------------+------------+
|           29760021 | California |
+--------------------+------------+
1 row in set (0.00 sec)

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








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