MySQL Developer

1.The mysql Client Program　　2.Data Types　　3.Joins　　4.Subqueries　　5.Views　　6.Stored Routine　　.

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1.Client/Server Concepts

1. Connection Parameter Options

   --host=host_name or -h host_name
       The default host value is localhost.
   
   --port=port_number or -P port_number
       The default MySQL port number is 3306.
   
   --user=user_name or -u user_name
       On Windows, the default MySQL account name is ODBC. On Unix, client programs use your system login name as your default MySQL account username.
   
   --password=pass_value or -ppass_value
   
   --compress or -C

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   You can also provide a database name to select that database as the default database.

   shell> mysql -u user_name -p -h host_name db_name

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2. Using Option Files
   • On Windows, programs look for option files in the following order: my.ini and my.cnf in the Windows directory(C:\Windows or C:\WinNT), and then C:\my.ini and C:\my.cnf.
   • On Unix, the file /etc/my.cnf serves as a global option file used by all users. Also, you can set up your own user-specific option file by creating a file named .my or .cnf in your home directory. If both exist, the global file is read first.
   • Create an option file

     [client]
     host = argor.com
     port = 3306
     compress
     
     [mysql]
     
     [mysqld]
     port = 3306
     basedir=""
     datadir=""

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     To create or modify an option file, you must have write permission for it. Client programs need only read access.

   • To tell a program to read a single specific option file instead of the standard option files, use the --defaults-file=file_name option as the first option on the command line.

     C:\Users\Administrator>type develop.ini
     [mysql]
     host=localhost
     port=3306
     user=develop
     password=develop
     compress
     default-character-set=utf8
     C:\Users\Administrator>mysql --defaults-file=develop.ini
     Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
     
     mysql>

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3. Using the --safe-updates Option

   --safe-updates has the following effects:
   
   1.UPDATE and DELETE statements are allowed only if they include a WHERE clause that specifically identifies which records to update or delete by means of a key value, or if they include a LIMIT clause.
   
   2.Output from single-table SELECT statement is restricted to no more 1,000 rows unless the statement includes a LIMIT clause.
   
   3.Multiple-table SELECT statements are allowed only if MySQL will examine no more than 1,000,000 rows to process the query.

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2.Data Types

1. INT

   Storage Required
       4 bytes
   
   Signed Range
       -2,147,683,648 to 2,147,483,647
   
   Unsigned Range
       0 to 4,294,967,295

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2. Floating-Point Data Types
   The following definition specify a single-precision column with a precision of 10 digits and scale of 3 decimals, and a double-precision column with a precision of 20 digits and scale of 7 decimals.

   weight FLOAT(10, 3)
   avg_score DOUBLE(20, 7)

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   The stored values are approximate.

3. Fixed-Point Data Types

 

3.Joins

1. Writing Inner Joins
   A join that identifies combinations of matching rows from two tables is called an inner join.
   
   • Writing Inner Joins with the Comma Operator
     A query to display languages and full country names can be written as a join that matches the country codes in the CountryLanguage table with those in the Country table.
     

     select
         name,language
     from
         ContryLanguage,Country
     where
         CountryCode = Code;

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   • Writing Inner Joins with INNER JOIN

     select
         name,language
     from
         ContryLanguage inner join Country
     on
         CountryCode = Code;

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     If the name of the joined column is the same in both tables, you can add USING() rather than ON after the table names, and list the name within the parentheses.

     select
         name,language
     from
         ContryLanguage inner join Country
     using(Code);

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     If you're joining the tables using more than one pair of like-named columns, list the column names within the parentheses of the USING() clause separated by commas.

      

2. Writing Outer Joins
   To write a join that proides information about mismatches or missing records, use an outer join.
   
   • Writing LEFT JOIN Queres
     A left join treats the left table (the first one named) as a reference table and produces output for each row selected from it, whether or not the row is matched by rows in the right tables.

     select
         name,language
     from
         Contry left join CountryLanguage
     on
         Code = CountryCode;
     
     select
         name,language
     from
         Contry left join CountryLanguage
     using(Code);

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   • Writing RIGHT JOIN Queries

4.Subqueries

A subquery is a SELECT statement that is placed within parentheses inside another SQL statement.

1. Types of Subqueries
   
   • Scalar subqueries return a single value; that is, one row with one column of data.
   • Row subqueries return a single row with one or more columns of data.
   • Column subqueries return a single column with one or more rows of data.
   • Table subqueries return a result with one or more rows containing one or more rows containing one or more columns of data.
2. Subqueries as Scalar Expressions
   

   select
       concat('The country code for Finland is: ',
           (select
               Code
           from
               Country
           where
               Name = 'Finland'
           )) as s1;
   
   select
       (select sum(Population) from city)
       /
       (select sum(Population) from Country) as ratio;

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   A scalar subquery result can be assigned to a user variable for later use. The previous example can be written with user variables as follows:

   set @city_pop = (select sum(Population) from city);
   set @country_pop = (select sum(Population) from country);
   select @city_pop / @country_pop as s2;

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3. Correlated Subqueries
   Subqueries can be non-correlated or correlated.
   
   In the following correlated subquery, we calculate which country on each populated continent has the argest population. The value of the column Continent, which appears in the outer query, is used to limit which rows to consider for the MAX() calculation in the subquery:

   select
       Continent, Name, Population
   from
       Country c
   where
       Population = (
                       select MAX(Population)
                       from Country c2
                       where c.Continent = c2.Continent and Population > 0
                   );

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4. Comparing Subquery Results to Outer Query Columns
   The scalar subquery examples shown in previous sections use the = equality operator to compare a single column to the value returned by the subquery. But you are not limited to using the = equality operator.
   When comparing the values in the outer query with those returned by a scalar subquery, you can use any of the usual comparison operators, such as =,<,>,<>, and >=.
   • Using ALL, ANY, and SOME
     To perform a comparison between a scalar value and a subquery that returns severval rows of data in a single column (a column subquery), we must use a quantified comparison. The quantifier keywords ALL, ANY, and SOME allow comparison to multiple-row results.
     
     Now, suppose that wo would like to know all the countries in the world where the population is larger than the average country population of all of the world's continents. To get this information, we can use ALL in conjunction with the > operator to compare the values of the country population with every average continent population from the preceding result:

     select
         Name, Population
     from
         Country
     where
         Population > ALL (
                             select avg(Population) from Country
                             group by
                                 Continent
                         )
     Order by
         Name;

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     The keyword ANY is not limited to working with the = operator. Any of the standard comparison operators (=,<,>,<>,>=, and so forth) may be used for the comparison.
     The following example finds the countries on the European continent, and, for each one, tests whether the country is among the worldwide list of countries where Spanish is spoken:

     select
         Name
     from
         Country
     where
         Continent = 'Europe'
         AND Code = ANY (
                         select CountryCode
                         from CountryLanguage
                         where Language = 'Spanish'
                     )
     order by
         Name;

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   • Using IN
     When IN is used with a subquery, it is functionally equivalent to = ANY (note that the = sign is part of the equivalence).

     select
         Name
     from
         Country
     where
         Continent = 'Europe'
         AND Code IN (
                     select CountryCode
                     from CountryLanguage
                     where Language = 'Spanish'
                     )
     order by
         Name;

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   • Using EXISTS
     The EXISTS predicate performs a simple test: It tells you whether the subquery finds any rows. It does not return the actual values found in any of the rows, it merely returns TRUE if any rows were found.

     select
         Code c, Name
     from
         Country
     where
         Continent = 'Europe'
         AND EXISTS (
                     select *
                     from CountryLanguage
                     where CountryCode = c
                         AND Language = 'Spanish'
                     );

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5. Comparison Using Row Subqueries
   For row subqueries, we can perform an equality comparison for all columns in a row. The subquery must return a single row.

   select
       City.Name
   from
       City
   where
       (City.ID, City.CountryCode) = (
                                       select Capital, Code
                                       from Country
                                       where Name = 'Finland'
                                   );

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   select
       Name, Population
   from
       Country
   where
       (Continent, Region) = ('Europe', 'Western Europe');

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6. Using Subqueries in the FROM Clause
   

   select
       avg(cont_sum)
   from (
           select Continent, sum(Population) as cont_sum
           from Country
           group by Continent
       ) as t;

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7. Converting Subqueries to Joins
   • Converting Subqueries to Inner Joins

     select
         Name
     from
         Country
     where
         Code IN (select CountryCode from CountryLanguage);
     
     select
         DISTINCT Name
     from
         Country, CountryLanguage
     where
         Code = CountryCode;

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   • Converting Subqueries to Outer Joins

     select
         Name
     from
         Country
     where
         Code NOT IN (select CountryCode from CountryLanguage);
     
     select
         Name
     from
         Country LEFT JOIN CountryLanguage
     on
         Code = CountryCode
     where
         CountryCode IS NULL;

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5.Views

1. Creating Views
   The name of the second column is COUNT(Language), which must be referred to using a quoted identifier (that is, as `COUNT(Language)`). To avoid this, provide names for the columns by including a column list in the view definition.
   Another way to provide names for view columns is by using column aliases in the SELECT statement.
   

   create
       view 'CountryLangCount'
       as
   (
       select Name, count(Language)
       from Country, CountryLanguage
       where Code = CountryCode
       group by Name
   );
   
   create
       view 'CountryLangCount' (Name, LangCount)
       as
   (
       select Name, count(Language)
       from Country, CountryLanguage
       where Code = CountryCode
       group by Name
   );
   
   create
       view 'CountryLangCount'
       as
   (
       select Name, count(Language) as LangCount
       from Country, CountryLanguage
       where Code = CountryCode
       group by Name
   );

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6.Stored Routine

1. Differences Between Stored Procedures and Functions
   The most general difference between procedures and functions is that they are invoked differently and for different purposes:
   • A procedure does not return a value. It is invoked with a CALL statement.
   • A function is invoked within an expression and returns a single value directly to the caller to be used in the expression.

 

 

 

 

MySQL Developer .