YOUR WEBSITE

          By default, the rows in the result set produced by a SELECT statement are returned by the server to the  client in no particular order.  When a query is issued, the server is free to return the rows in any convenient  order.  This order can be affected by factors such as the order in which the rows are actually stored in the  table, or which indexes are used to process the query.  If the output rows need to be returned in a specific  order, include an ORDER BY clause that indicates how to sort the results.  There is no guarantee about the order in which the server returns rows, unless the order is specified.  To do  so, add an ORDER BY clause to the statement that defines the sort order desired.  Single Column Sorts  The following example returns country names (in the Country table of the world database) alphabetically  by Country Name;  mysql> SELECT Name FROM Country ORDER BY Name;  +------------------------------+  | Name                            |  +--------

The WHERE clause is the mechanism for filtering out unwanted rows from the result set.  Rows can be  selected by looking for column values that satisfy various criteria, and different types of values can be  filtered out.  In the statement below, the query is selecting information from three columns,  from a given  table with a clause  where a specific city name is to be used. In other words, it is answering the  question…"What is the ID and district for the city of New York?", as follows;  mysql> SELECT ID, Name, District FROM City           -> WHERE Name = 'New York';  +-------+--------------+-------------+  | ID      | Name        | District     |  +-------+--------------+--------------+  | 3793 | New York | New York  |  +-------+--------------+--------------+   1 row in set (#.## sec)  Expressions in WHERE clauses can use the following types of operators;  ƒ                              Arithmetic -- for calculation  ƒ

I f a query returns a result that contains duplicate rows, the duplicates can be removed to produce a result set  in which every row is unique.  To do this, include the clause DISTINCT after SELECT and before the  column list.  Caution needs to be present when using DISTINCT due to the fact that DISTINCT will  compare whole rows when processing.  In the case below, the query results in a set that includes duplicate  rows:  mysql> SELECT Continent FROM Country;  +--------------------+  | Continent          |  +--------------------+  | Asia                  |  | Europe             |  | North America |  | Europe             |  | Africa                |  | Oceania           |         ...       | Antarctica        |  | Oceania           |  +--------------------+  239 rows in set (#.## sec)  By adding DISTINCT to the statement, the duplicates are removed and only unique rows are returned:  mysql> SELECT DISTINCT Continent FROM Country; 

            There are many clauses, and combinations thereof, that can be used with a SELECT statement to yield  particular table query results.  They range from very basic, commonly-used options to very specialized and  complex.  The following basic, optional clauses will be covered in this section:  Clauses                   Definition DISTINCT                Eliminates duplicate row data  FROM                      Specifies what table(s) to retrieve data from  WHERE                   Decides what data to show  ORDER BY             Sorts data by specified order criteria  LIMIT                        Reduces the amount of records received  Example of SELECT statement with clauses:  SELECT DISTINCT values_to_display FROM table_name WHERE expression ORDER BY how_to_sort LIMIT row_count;               The above syntax shows the correct order and usage of each of the above optional clauses.  This statement is specifically  selecting  distinct data rows  from a named ta

The  SELECT statement is primarily used to retrieve zero or more  rows from one or more tables in a  database.  In MySQL,  SELECT is the most commonly used DML (Data Manipulation Language)  command.  In specifying a SELECT query, the user specifies a description of the desired result set.  It is  built with optional clauses that specify how and what data to retrieve.  The general command syntax is  shown below;  SELECT [<clause options>] <column list> [FROM] <table>  [<clause options>];  Basic SELECT statement example using world database (and the result data):  mysql> SELECT Name FROM Country;  +-------------------------------------------------+  | Name                                                    |  +-------------------------------------------------+  | Afghanistan                                          |  | Netherlands                                          |  | Netherlands Antilles                            |  | Albania        

The FOREIGN KEY clause has several parts:   •  It names the column in the referring table (country_code).   •  It names the code column in the country_parent table as the referenced column. This column is  the “foreign” key.   •  It specifies what actions to take if records are modified in the referenced table. The foreign key  definition shown specifies the  CASCADE action for both  UPDATE and  DELETE operations. This  means that changes in the parent table are cascaded down to the child table. If a  code value is  changed in the  country_parent table, InnoDB changes any corresponding  city_child  records with that value in the country_code column to match. If a country_parent record is  deleted, InnoDB also deletes any  city_child records with the same country code. (InnoDB  supports actions other than CASCADE, but they are not covered here.   Instead of  CASCADE a SET NULL or RESTRICT can be specified.  In a foreign key relationship, the referring column and the

A foreign key relationship allows for the declaration of an index in one table to be related to an index in  another.  It also allows for the placing of constraints on what may be done to the tables in the relationship.   The database enforces the rules of this relationship to maintain referential integrity.  Using Foreign Keys with InnoDB  The InnoDB storage engine supports the use of foreign keys (unlike other storage engines).  This capability  enables the declaration of relationships between columns in different tables, and InnoDB maintains  integrity between the tables by prohibiting operations that violate those relationships.  For example, the  following restrictions must be addressed:   •  A table must contain only records with ID values that are known in another reference table.   •  If an ID in the referenced table is changed, the ID in all matching records in the referencing table  must be changed to match.   •  If a record with a given ID in the referenced t