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Cleanup of MySQL-Max description 


Docs/manual.texi:
  Moved things in example section.
  Added some links from user comments.
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Docs/manual.texi
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...@@ -538,29 +538,18 @@ MySQL Tutorial ...@@ -538,29 +538,18 @@ MySQL Tutorial
* Connecting-disconnecting:: Connecting to and disconnecting from the server * Connecting-disconnecting:: Connecting to and disconnecting from the server
* Entering queries:: Entering queries * Entering queries:: Entering queries
* Examples:: Examples
* Searching on two keys:: Searching on two keys
* Database use:: Creating and using a database * Database use:: Creating and using a database
* Getting information:: Getting information about databases and tables * Getting information:: Getting information about databases and tables
* Examples:: Examples
* Batch mode:: Using @code{mysql} in batch mode * Batch mode:: Using @code{mysql} in batch mode
* Twin:: Queries from twin project * Twin:: Queries from twin project
Examples of Common Queries
* example-Maximum-column:: The maximum value for a column
* example-Maximum-row:: The row holding the maximum of a certain column
* example-Maximum-column-group:: Maximum of column per group
* example-Maximum-column-group-row:: The rows holding the group-wise maximum of a certain field
* example-user-variables:: Using user variables
* example-Foreign keys:: Using foreign keys
Creating and Using a Database Creating and Using a Database
* Creating database:: Creating a database * Creating database:: Creating a database
* Creating tables:: Creating a table * Creating tables:: Creating a table
* Loading tables:: Loading data into a table * Loading tables:: Loading data into a table
* Retrieving data:: Retrieving information from a table * Retrieving data:: Retrieving information from a table
* Multiple tables:: Using more than one table
Retrieving Information from a Table Retrieving Information from a Table
...@@ -572,6 +561,17 @@ Retrieving Information from a Table ...@@ -572,6 +561,17 @@ Retrieving Information from a Table
* Working with NULL:: Working with @code{NULL} values * Working with NULL:: Working with @code{NULL} values
* Pattern matching:: Pattern matching * Pattern matching:: Pattern matching
* Counting rows:: Counting rows * Counting rows:: Counting rows
* Multiple tables::
Examples of Common Queries
* example-Maximum-column:: The maximum value for a column
* example-Maximum-row:: The row holding the maximum of a certain column
* example-Maximum-column-group:: Maximum of column per group
* example-Maximum-column-group-row:: The rows holding the group-wise maximum of a certain field
* example-user-variables:: Using user variables
* example-Foreign keys:: Using foreign keys
* Searching on two keys::
Queries from Twin Project Queries from Twin Project
...@@ -2486,8 +2486,14 @@ which services were discovered on which dial-up numbers in your organization. ...@@ -2486,8 +2486,14 @@ which services were discovered on which dial-up numbers in your organization.
@subheading SQL Clients and Report Writers @subheading SQL Clients and Report Writers
@table @asis @table @asis
@item @uref{http://www.urbanresearch.com/software/utils/urbsql/index.html} @item @uref{http://www.urbanresearch.com/software/utils/urbsql/index.html, urSQL}
@strong{MySQL} Editor/Utility for MS Windows Platforms. SQL Editor and Query Utility. Custom syntax highlighting, editable
results grid, exportable result-sets, basic @strong{MySQL} admin functions,
Etc.. For windows.
@item @uref{http://www.edatanew.com/, MySQL Data Manager}
@strong{MySQL} Data Manager * is platform independent web client
(written in perl) for @strong{MySQL} server over TCP/IP.
@item @uref{http://ksql.sourceforge.net/} @item @uref{http://ksql.sourceforge.net/}
KDE @strong{MySQL} client. KDE @strong{MySQL} client.
...@@ -24429,10 +24435,9 @@ Innodb table space will not be reclaimed. ...@@ -24429,10 +24435,9 @@ Innodb table space will not be reclaimed.
@menu @menu
* Connecting-disconnecting:: Connecting to and disconnecting from the server * Connecting-disconnecting:: Connecting to and disconnecting from the server
* Entering queries:: Entering queries * Entering queries:: Entering queries
* Examples:: Examples
* Searching on two keys:: Searching on two keys
* Database use:: Creating and using a database * Database use:: Creating and using a database
* Getting information:: Getting information about databases and tables * Getting information:: Getting information about databases and tables
* Examples:: Examples
* Batch mode:: Using @code{mysql} in batch mode * Batch mode:: Using @code{mysql} in batch mode
* Twin:: Queries from twin project * Twin:: Queries from twin project
@end menu @end menu
...@@ -24532,7 +24537,7 @@ server. They indicate this by the @code{mysql>} prompt. ...@@ -24532,7 +24537,7 @@ server. They indicate this by the @code{mysql>} prompt.
@cindex running, queries @cindex running, queries
@cindex queries, entering @cindex queries, entering
@cindex entering, queries @cindex entering, queries
@node Entering queries, Examples, Connecting-disconnecting, Tutorial @node Entering queries, Database use, Connecting-disconnecting, Tutorial
@section Entering Queries @section Entering Queries
Make sure you are connected to the server, as discussed in the previous Make sure you are connected to the server, as discussed in the previous
...@@ -24754,358 +24759,10 @@ containing @code{QUIT}! This can be quite confusing, especially if you ...@@ -24754,358 +24759,10 @@ containing @code{QUIT}! This can be quite confusing, especially if you
don't know that you need to supply the terminating quote before you can don't know that you need to supply the terminating quote before you can
cancel the current command. cancel the current command.
@cindex queries, examples
@cindex examples, queries
@node Examples, Searching on two keys, Entering queries, Tutorial
@section Examples of Common Queries
Here are examples of how to solve some common problems with
@strong{MySQL}.
Some of the examples use the table @code{shop} to hold the price of each
article (item number) for certain traders (dealers). Supposing that each
trader has a single fixed price per article, then (@code{item},
@code{trader}) is a primary key for the records.
Start the command line tool @code{mysql} and select a database:
@example
mysql your-database-name
@end example
(In most @strong{MySQL} installations, you can use the database-name 'test').
You can create the example table as:
@example
CREATE TABLE shop (
article INT(4) UNSIGNED ZEROFILL DEFAULT '0000' NOT NULL,
dealer CHAR(20) DEFAULT '' NOT NULL,
price DOUBLE(16,2) DEFAULT '0.00' NOT NULL,
PRIMARY KEY(article, dealer));
INSERT INTO shop VALUES
(1,'A',3.45),(1,'B',3.99),(2,'A',10.99),(3,'B',1.45),(3,'C',1.69),
(3,'D',1.25),(4,'D',19.95);
@end example
Okay, so the example data is:
@example
mysql> SELECT * FROM shop;
+---------+--------+-------+
| article | dealer | price |
+---------+--------+-------+
| 0001 | A | 3.45 |
| 0001 | B | 3.99 |
| 0002 | A | 10.99 |
| 0003 | B | 1.45 |
| 0003 | C | 1.69 |
| 0003 | D | 1.25 |
| 0004 | D | 19.95 |
+---------+--------+-------+
@end example
@menu
* example-Maximum-column:: The maximum value for a column
* example-Maximum-row:: The row holding the maximum of a certain column
* example-Maximum-column-group:: Maximum of column per group
* example-Maximum-column-group-row:: The rows holding the group-wise maximum of a certain field
* example-user-variables:: Using user variables
* example-Foreign keys:: Using foreign keys
@end menu
@node example-Maximum-column, example-Maximum-row, Examples, Examples
@subsection The Maximum Value for a Column
``What's the highest item number?''
@example
SELECT MAX(article) AS article FROM shop
+---------+
| article |
+---------+
| 4 |
+---------+
@end example
@node example-Maximum-row, example-Maximum-column-group, example-Maximum-column, Examples
@subsection The Row Holding the Maximum of a Certain Column
``Find number, dealer, and price of the most expensive article.''
In ANSI SQL this is easily done with a sub-query:
@example
SELECT article, dealer, price
FROM shop
WHERE price=(SELECT MAX(price) FROM shop)
@end example
In @strong{MySQL} (which does not yet have sub-selects), just do it in
two steps:
@enumerate
@item
Get the maximum price value from the table with a @code{SELECT} statement.
@item
Using this value compile the actual query:
@example
SELECT article, dealer, price
FROM shop
WHERE price=19.95
@end example
@end enumerate
Another solution is to sort all rows descending by price and only
get the first row using the @strong{MySQL} specific @code{LIMIT} clause:
@example
SELECT article, dealer, price
FROM shop
ORDER BY price DESC
LIMIT 1
@end example
@strong{NOTE}: If there are several most expensive articles (for example, each 19.95)
the @code{LIMIT} solution shows only one of them!
@node example-Maximum-column-group, example-Maximum-column-group-row, example-Maximum-row, Examples
@subsection Maximum of Column per Group
``What's the highest price per article?''
@example
SELECT article, MAX(price) AS price
FROM shop
GROUP BY article
+---------+-------+
| article | price |
+---------+-------+
| 0001 | 3.99 |
| 0002 | 10.99 |
| 0003 | 1.69 |
| 0004 | 19.95 |
+---------+-------+
@end example
@node example-Maximum-column-group-row, example-user-variables, example-Maximum-column-group, Examples
@subsection The Rows Holding the Group-wise Maximum of a Certain Field
``For each article, find the dealer(s) with the most expensive price.''
In ANSI SQL, I'd do it with a sub-query like this:
@example
SELECT article, dealer, price
FROM shop s1
WHERE price=(SELECT MAX(s2.price)
FROM shop s2
WHERE s1.article = s2.article);
@end example
In @strong{MySQL} it's best do it in several steps:
@enumerate
@item
Get the list of (article,maxprice).
@item
For each article get the corresponding rows that have the stored maximum
price.
@end enumerate
This can easily be done with a temporary table:
@example
CREATE TEMPORARY TABLE tmp (
article INT(4) UNSIGNED ZEROFILL DEFAULT '0000' NOT NULL,
price DOUBLE(16,2) DEFAULT '0.00' NOT NULL);
LOCK TABLES shop read;
INSERT INTO tmp SELECT article, MAX(price) FROM shop GROUP BY article;
SELECT shop.article, dealer, shop.price FROM shop, tmp
WHERE shop.article=tmp.article AND shop.price=tmp.price;
UNLOCK TABLES;
DROP TABLE tmp;
@end example
If you don't use a @code{TEMPORARY} table, you must also lock the 'tmp' table.
``Can it be done with a single query?''
Yes, but only by using a quite inefficient trick that I call the
``MAX-CONCAT trick'':
@example
SELECT article,
SUBSTRING( MAX( CONCAT(LPAD(price,6,'0'),dealer) ), 7) AS dealer,
0.00+LEFT( MAX( CONCAT(LPAD(price,6,'0'),dealer) ), 6) AS price
FROM shop
GROUP BY article;
+---------+--------+-------+
| article | dealer | price |
+---------+--------+-------+
| 0001 | B | 3.99 |
| 0002 | A | 10.99 |
| 0003 | C | 1.69 |
| 0004 | D | 19.95 |
+---------+--------+-------+
@end example
The last example can, of course, be made a bit more efficient by doing the
splitting of the concatenated column in the client.
@node example-user-variables, example-Foreign keys, example-Maximum-column-group-row, Examples
@subsection Using user variables
You can use @strong{MySQL} user variables to remember results without
having to store them in a temporary variables in the client.
@xref{Variables}.
For example, to find the articles with the highest and lowest price you
can do:
@example
select @@min_price:=min(price),@@max_price:=max(price) from shop;
select * from shop where price=@@min_price or price=@@max_price;
+---------+--------+-------+
| article | dealer | price |
+---------+--------+-------+
| 0003 | D | 1.25 |
| 0004 | D | 19.95 |
+---------+--------+-------+
@end example
@cindex foreign keys
@cindex keys, foreign
@node example-Foreign keys, , example-user-variables, Examples
@subsection Using Foreign Keys
You don't need foreign keys to join 2 tables.
The only thing @strong{MySQL} doesn't do is @code{CHECK} to make sure that
the keys you use really exist in the table(s) you're referencing and it
doesn't automatically delete rows from table with a foreign key
definition. If you use your keys like normal, it'll work just fine:
@example
CREATE TABLE persons (
id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT,
name CHAR(60) NOT NULL,
PRIMARY KEY (id)
);
CREATE TABLE shirts (
id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT,
style ENUM('t-shirt', 'polo', 'dress') NOT NULL,
color ENUM('red', 'blue', 'orange', 'white', 'black') NOT NULL,
owner SMALLINT UNSIGNED NOT NULL REFERENCES persons,
PRIMARY KEY (id)
);
INSERT INTO persons VALUES (NULL, 'Antonio Paz');
INSERT INTO shirts VALUES
(NULL, 'polo', 'blue', LAST_INSERT_ID()),
(NULL, 'dress', 'white', LAST_INSERT_ID()),
(NULL, 't-shirt', 'blue', LAST_INSERT_ID());
INSERT INTO persons VALUES (NULL, 'Lilliana Angelovska');
INSERT INTO shirts VALUES
(NULL, 'dress', 'orange', LAST_INSERT_ID()),
(NULL, 'polo', 'red', LAST_INSERT_ID()),
(NULL, 'dress', 'blue', LAST_INSERT_ID()),
(NULL, 't-shirt', 'white', LAST_INSERT_ID());
SELECT * FROM persons;
+----+---------------------+
| id | name |
+----+---------------------+
| 1 | Antonio Paz |
| 2 | Lilliana Angelovska |
+----+---------------------+
SELECT * FROM shirts;
+----+---------+--------+-------+
| id | style | color | owner |
+----+---------+--------+-------+
| 1 | polo | blue | 1 |
| 2 | dress | white | 1 |
| 3 | t-shirt | blue | 1 |
| 4 | dress | orange | 2 |
| 5 | polo | red | 2 |
| 6 | dress | blue | 2 |
| 7 | t-shirt | white | 2 |
+----+---------+--------+-------+
SELECT s.* FROM persons p, shirts s
WHERE p.name LIKE 'Lilliana%'
AND s.owner = p.id
AND s.color <> 'white';
+----+-------+--------+-------+
| id | style | color | owner |
+----+-------+--------+-------+
| 4 | dress | orange | 2 |
| 5 | polo | red | 2 |
| 6 | dress | blue | 2 |
+----+-------+--------+-------+
@end example
@findex UNION
@cindex searching, two keys
@cindex keys, searching on two
@node Searching on two keys, Database use, Examples, Tutorial
@section Searching on Two Keys
@strong{MySQL} doesn't yet optimize when you search on two different
keys combined with @code{OR} (Searching on one key with different @code{OR}
parts is optimized quite good):
@example
SELECT field1_index, field2_index FROM test_table WHERE field1_index = '1'
OR field2_index = '1'
@end example
The reason is that we haven't yet had time to come up with an efficient
way to handle this in the general case. (The @code{AND} handling is,
in comparison, now completely general and works very well).
For the moment you can solve this very efficiently by using a
@code{TEMPORARY} table. This type of optimization is also very good if
you are using very complicated queries where the SQL server does the
optimizations in the wrong order.
@example
CREATE TEMPORARY TABLE tmp
SELECT field1_index, field2_index FROM test_table WHERE field1_index = '1';
INSERT INTO tmp
SELECT field1_index, field2_index FROM test_table WHERE field2_index = '1';
SELECT * from tmp;
DROP TABLE tmp;
@end example
The above way to solve this query is in effect an @code{UNION} of two queries.
@cindex databases, creating @cindex databases, creating
@cindex databases, using @cindex databases, using
@cindex creating, databases @cindex creating, databases
@node Database use, Getting information, Searching on two keys, Tutorial @node Database use, Getting information, Entering queries, Tutorial
@section Creating and Using a Database @section Creating and Using a Database
@menu @menu
...@@ -25113,7 +24770,6 @@ The above way to solve this query is in effect an @code{UNION} of two queries. ...@@ -25113,7 +24770,6 @@ The above way to solve this query is in effect an @code{UNION} of two queries.
* Creating tables:: Creating a table * Creating tables:: Creating a table
* Loading tables:: Loading data into a table * Loading tables:: Loading data into a table
* Retrieving data:: Retrieving information from a table * Retrieving data:: Retrieving information from a table
* Multiple tables:: Using more than one table
@end menu @end menu
Now that you know how to enter commands, it's time to access a database. Now that you know how to enter commands, it's time to access a database.
...@@ -25416,7 +25072,7 @@ than a single @code{LOAD DATA} statement. ...@@ -25416,7 +25072,7 @@ than a single @code{LOAD DATA} statement.
@cindex tables, retrieving data @cindex tables, retrieving data
@cindex retrieving, data from tables @cindex retrieving, data from tables
@cindex unloading, tables @cindex unloading, tables
@node Retrieving data, Multiple tables, Loading tables, Database use @node Retrieving data, , Loading tables, Database use
@subsection Retrieving Information from a Table @subsection Retrieving Information from a Table
@menu @menu
...@@ -25428,6 +25084,7 @@ than a single @code{LOAD DATA} statement. ...@@ -25428,6 +25084,7 @@ than a single @code{LOAD DATA} statement.
* Working with NULL:: Working with @code{NULL} values * Working with NULL:: Working with @code{NULL} values
* Pattern matching:: Pattern matching * Pattern matching:: Pattern matching
* Counting rows:: Counting rows * Counting rows:: Counting rows
* Multiple tables::
@end menu @end menu
The @code{SELECT} statement is used to pull information from a table. The @code{SELECT} statement is used to pull information from a table.
...@@ -26150,7 +25807,7 @@ mysql> SELECT * FROM pet WHERE name REGEXP "^.@{5@}$"; ...@@ -26150,7 +25807,7 @@ mysql> SELECT * FROM pet WHERE name REGEXP "^.@{5@}$";
@cindex rows, counting @cindex rows, counting
@cindex tables, counting rows @cindex tables, counting rows
@cindex counting, table rows @cindex counting, table rows
@node Counting rows, , Pattern matching, Retrieving data @node Counting rows, Multiple tables, Pattern matching, Retrieving data
@subsubsection Counting Rows @subsubsection Counting Rows
Databases are often used to answer the question, ``How often does a certain Databases are often used to answer the question, ``How often does a certain
...@@ -26286,8 +25943,8 @@ mysql> SELECT species, sex, COUNT(*) FROM pet ...@@ -26286,8 +25943,8 @@ mysql> SELECT species, sex, COUNT(*) FROM pet
@end example @end example
@cindex tables, multiple @cindex tables, multiple
@node Multiple tables, , Retrieving data, Database use @node Multiple tables, , Counting rows, Retrieving data
@subsection Using More Than one Table @subsubsection Using More Than one Table
The @code{pet} table keeps track of which pets you have. If you want to The @code{pet} table keeps track of which pets you have. If you want to
record other information about them, such as events in their lives like record other information about them, such as events in their lives like
...@@ -26408,7 +26065,7 @@ each column reference is associated with. ...@@ -26408,7 +26065,7 @@ each column reference is associated with.
@cindex databases, information about @cindex databases, information about
@cindex tables, information about @cindex tables, information about
@findex DESCRIBE @findex DESCRIBE
@node Getting information, Batch mode, Database use, Tutorial @node Getting information, Examples, Database use, Tutorial
@section Getting Information About Databases and Tables @section Getting Information About Databases and Tables
What if you forget the name of a database or table, or what the structure of What if you forget the name of a database or table, or what the structure of
...@@ -26469,12 +26126,361 @@ indexed, and @code{Default} specifies the column's default value. ...@@ -26469,12 +26126,361 @@ indexed, and @code{Default} specifies the column's default value.
If you have indexes on a table, If you have indexes on a table,
@code{SHOW INDEX FROM tbl_name} produces information about them. @code{SHOW INDEX FROM tbl_name} produces information about them.
@cindex queries, examples
@cindex examples, queries
@node Examples, Batch mode, Getting information, Tutorial
@section Examples of Common Queries
Here are examples of how to solve some common problems with
@strong{MySQL}.
Some of the examples use the table @code{shop} to hold the price of each
article (item number) for certain traders (dealers). Supposing that each
trader has a single fixed price per article, then (@code{item},
@code{trader}) is a primary key for the records.
Start the command line tool @code{mysql} and select a database:
@example
mysql your-database-name
@end example
(In most @strong{MySQL} installations, you can use the database-name 'test').
You can create the example table as:
@example
CREATE TABLE shop (
article INT(4) UNSIGNED ZEROFILL DEFAULT '0000' NOT NULL,
dealer CHAR(20) DEFAULT '' NOT NULL,
price DOUBLE(16,2) DEFAULT '0.00' NOT NULL,
PRIMARY KEY(article, dealer));
INSERT INTO shop VALUES
(1,'A',3.45),(1,'B',3.99),(2,'A',10.99),(3,'B',1.45),(3,'C',1.69),
(3,'D',1.25),(4,'D',19.95);
@end example
Okay, so the example data is:
@example
mysql> SELECT * FROM shop;
+---------+--------+-------+
| article | dealer | price |
+---------+--------+-------+
| 0001 | A | 3.45 |
| 0001 | B | 3.99 |
| 0002 | A | 10.99 |
| 0003 | B | 1.45 |
| 0003 | C | 1.69 |
| 0003 | D | 1.25 |
| 0004 | D | 19.95 |
+---------+--------+-------+
@end example
@menu
* example-Maximum-column:: The maximum value for a column
* example-Maximum-row:: The row holding the maximum of a certain column
* example-Maximum-column-group:: Maximum of column per group
* example-Maximum-column-group-row:: The rows holding the group-wise maximum of a certain field
* example-user-variables:: Using user variables
* example-Foreign keys:: Using foreign keys
* Searching on two keys::
@end menu
@node example-Maximum-column, example-Maximum-row, Examples, Examples
@subsection The Maximum Value for a Column
``What's the highest item number?''
@example
SELECT MAX(article) AS article FROM shop
+---------+
| article |
+---------+
| 4 |
+---------+
@end example
@node example-Maximum-row, example-Maximum-column-group, example-Maximum-column, Examples
@subsection The Row Holding the Maximum of a Certain Column
``Find number, dealer, and price of the most expensive article.''
In ANSI SQL this is easily done with a sub-query:
@example
SELECT article, dealer, price
FROM shop
WHERE price=(SELECT MAX(price) FROM shop)
@end example
In @strong{MySQL} (which does not yet have sub-selects), just do it in
two steps:
@enumerate
@item
Get the maximum price value from the table with a @code{SELECT} statement.
@item
Using this value compile the actual query:
@example
SELECT article, dealer, price
FROM shop
WHERE price=19.95
@end example
@end enumerate
Another solution is to sort all rows descending by price and only
get the first row using the @strong{MySQL} specific @code{LIMIT} clause:
@example
SELECT article, dealer, price
FROM shop
ORDER BY price DESC
LIMIT 1
@end example
@strong{NOTE}: If there are several most expensive articles (for example, each 19.95)
the @code{LIMIT} solution shows only one of them!
@node example-Maximum-column-group, example-Maximum-column-group-row, example-Maximum-row, Examples
@subsection Maximum of Column per Group
``What's the highest price per article?''
@example
SELECT article, MAX(price) AS price
FROM shop
GROUP BY article
+---------+-------+
| article | price |
+---------+-------+
| 0001 | 3.99 |
| 0002 | 10.99 |
| 0003 | 1.69 |
| 0004 | 19.95 |
+---------+-------+
@end example
@node example-Maximum-column-group-row, example-user-variables, example-Maximum-column-group, Examples
@subsection The Rows Holding the Group-wise Maximum of a Certain Field
``For each article, find the dealer(s) with the most expensive price.''
In ANSI SQL, I'd do it with a sub-query like this:
@example
SELECT article, dealer, price
FROM shop s1
WHERE price=(SELECT MAX(s2.price)
FROM shop s2
WHERE s1.article = s2.article);
@end example
In @strong{MySQL} it's best do it in several steps:
@enumerate
@item
Get the list of (article,maxprice).
@item
For each article get the corresponding rows that have the stored maximum
price.
@end enumerate
This can easily be done with a temporary table:
@example
CREATE TEMPORARY TABLE tmp (
article INT(4) UNSIGNED ZEROFILL DEFAULT '0000' NOT NULL,
price DOUBLE(16,2) DEFAULT '0.00' NOT NULL);
LOCK TABLES shop read;
INSERT INTO tmp SELECT article, MAX(price) FROM shop GROUP BY article;
SELECT shop.article, dealer, shop.price FROM shop, tmp
WHERE shop.article=tmp.article AND shop.price=tmp.price;
UNLOCK TABLES;
DROP TABLE tmp;
@end example
If you don't use a @code{TEMPORARY} table, you must also lock the 'tmp' table.
``Can it be done with a single query?''
Yes, but only by using a quite inefficient trick that I call the
``MAX-CONCAT trick'':
@example
SELECT article,
SUBSTRING( MAX( CONCAT(LPAD(price,6,'0'),dealer) ), 7) AS dealer,
0.00+LEFT( MAX( CONCAT(LPAD(price,6,'0'),dealer) ), 6) AS price
FROM shop
GROUP BY article;
+---------+--------+-------+
| article | dealer | price |
+---------+--------+-------+
| 0001 | B | 3.99 |
| 0002 | A | 10.99 |
| 0003 | C | 1.69 |
| 0004 | D | 19.95 |
+---------+--------+-------+
@end example
The last example can, of course, be made a bit more efficient by doing the
splitting of the concatenated column in the client.
@node example-user-variables, example-Foreign keys, example-Maximum-column-group-row, Examples
@subsection Using user variables
You can use @strong{MySQL} user variables to remember results without
having to store them in a temporary variables in the client.
@xref{Variables}.
For example, to find the articles with the highest and lowest price you
can do:
@example
select @@min_price:=min(price),@@max_price:=max(price) from shop;
select * from shop where price=@@min_price or price=@@max_price;
+---------+--------+-------+
| article | dealer | price |
+---------+--------+-------+
| 0003 | D | 1.25 |
| 0004 | D | 19.95 |
+---------+--------+-------+
@end example
@cindex foreign keys
@cindex keys, foreign
@node example-Foreign keys, Searching on two keys, example-user-variables, Examples
@subsection Using Foreign Keys
You don't need foreign keys to join 2 tables.
The only thing @strong{MySQL} doesn't do is @code{CHECK} to make sure that
the keys you use really exist in the table(s) you're referencing and it
doesn't automatically delete rows from table with a foreign key
definition. If you use your keys like normal, it'll work just fine:
@example
CREATE TABLE persons (
id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT,
name CHAR(60) NOT NULL,
PRIMARY KEY (id)
);
CREATE TABLE shirts (
id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT,
style ENUM('t-shirt', 'polo', 'dress') NOT NULL,
color ENUM('red', 'blue', 'orange', 'white', 'black') NOT NULL,
owner SMALLINT UNSIGNED NOT NULL REFERENCES persons,
PRIMARY KEY (id)
);
INSERT INTO persons VALUES (NULL, 'Antonio Paz');
INSERT INTO shirts VALUES
(NULL, 'polo', 'blue', LAST_INSERT_ID()),
(NULL, 'dress', 'white', LAST_INSERT_ID()),
(NULL, 't-shirt', 'blue', LAST_INSERT_ID());
INSERT INTO persons VALUES (NULL, 'Lilliana Angelovska');
INSERT INTO shirts VALUES
(NULL, 'dress', 'orange', LAST_INSERT_ID()),
(NULL, 'polo', 'red', LAST_INSERT_ID()),
(NULL, 'dress', 'blue', LAST_INSERT_ID()),
(NULL, 't-shirt', 'white', LAST_INSERT_ID());
SELECT * FROM persons;
+----+---------------------+
| id | name |
+----+---------------------+
| 1 | Antonio Paz |
| 2 | Lilliana Angelovska |
+----+---------------------+
SELECT * FROM shirts;
+----+---------+--------+-------+
| id | style | color | owner |
+----+---------+--------+-------+
| 1 | polo | blue | 1 |
| 2 | dress | white | 1 |
| 3 | t-shirt | blue | 1 |
| 4 | dress | orange | 2 |
| 5 | polo | red | 2 |
| 6 | dress | blue | 2 |
| 7 | t-shirt | white | 2 |
+----+---------+--------+-------+
SELECT s.* FROM persons p, shirts s
WHERE p.name LIKE 'Lilliana%'
AND s.owner = p.id
AND s.color <> 'white';
+----+-------+--------+-------+
| id | style | color | owner |
+----+-------+--------+-------+
| 4 | dress | orange | 2 |
| 5 | polo | red | 2 |
| 6 | dress | blue | 2 |
+----+-------+--------+-------+
@end example
@findex UNION
@cindex searching, two keys
@cindex keys, searching on two
@node Searching on two keys, , example-Foreign keys, Examples
@subsection Searching on Two Keys
@strong{MySQL} doesn't yet optimize when you search on two different
keys combined with @code{OR} (Searching on one key with different @code{OR}
parts is optimized quite good):
@example
SELECT field1_index, field2_index FROM test_table WHERE field1_index = '1'
OR field2_index = '1'
@end example
The reason is that we haven't yet had time to come up with an efficient
way to handle this in the general case. (The @code{AND} handling is,
in comparison, now completely general and works very well).
For the moment you can solve this very efficiently by using a
@code{TEMPORARY} table. This type of optimization is also very good if
you are using very complicated queries where the SQL server does the
optimizations in the wrong order.
@example
CREATE TEMPORARY TABLE tmp
SELECT field1_index, field2_index FROM test_table WHERE field1_index = '1';
INSERT INTO tmp
SELECT field1_index, field2_index FROM test_table WHERE field2_index = '1';
SELECT * from tmp;
DROP TABLE tmp;
@end example
The above way to solve this query is in effect an @code{UNION} of two queries.
@cindex modes, batch @cindex modes, batch
@cindex batch mode @cindex batch mode
@cindex running, batch mode @cindex running, batch mode
@cindex script files @cindex script files
@cindex files, script @cindex files, script
@node Batch mode, Twin, Getting information, Tutorial @node Batch mode, Twin, Examples, Tutorial
@section Using @code{mysql} in Batch Mode @section Using @code{mysql} in Batch Mode
In the previous sections, you used @code{mysql} interactively to enter In the previous sections, you used @code{mysql} interactively to enter
...@@ -41240,6 +41246,10 @@ An online magazine featuring music, literature, arts, and design content. ...@@ -41240,6 +41246,10 @@ An online magazine featuring music, literature, arts, and design content.
@itemize @bullet @itemize @bullet
@item @uref{http://liftoff.msfc.nasa.gov, NASA}
@item @uref{http://kids.msfc.nasa.gov, NASA KIDS}
@item @uref{http://science.nasa.gov, Sience@@NASA}
@item @uref{http://lindev.jmc.tju.edu/qwor, Qt Widget and Object Repository} @item @uref{http://lindev.jmc.tju.edu/qwor, Qt Widget and Object Repository}
@item @uref{http://www.samba-choro.com.br, Brazilian samba site (in Portuguese)} @item @uref{http://www.samba-choro.com.br, Brazilian samba site (in Portuguese)}
...@@ -42108,6 +42118,10 @@ An authentication module for the Cyrus IMAP server. By Aaron Newsome. ...@@ -42108,6 +42118,10 @@ An authentication module for the Cyrus IMAP server. By Aaron Newsome.
@appendixsec Converters @appendixsec Converters
@itemize @bullet @itemize @bullet
item @uref{http://www.mysql.com/Downloads/Contrib/mssql2mysql.txt, mssql2mysql.txt}
Converter from MS-SQL to MySQL. By Michael Kofler.
@uref{http://www.kofler.cc/mysql/mssql2mysql.html, mssql2mysql home page}.
@item @uref{http://www.mysql.com/Downloads/Contrib/dbf2mysql-1.14.tar.gz, dbf2mysql-1.14.tar.gz} @item @uref{http://www.mysql.com/Downloads/Contrib/dbf2mysql-1.14.tar.gz, dbf2mysql-1.14.tar.gz}
Convert between @file{.dbf} files and @strong{MySQL} tables. By Maarten Convert between @file{.dbf} files and @strong{MySQL} tables. By Maarten
Boekhold (@email{boekhold@@cindy.et.tudelft.nl}), William Volkman, and Boekhold (@email{boekhold@@cindy.et.tudelft.nl}), William Volkman, and
support-files/mysql.spec.sh
View file @ cd260ea6
...@@ -17,6 +17,7 @@ Source: http://www.mysql.com/Downloads/MySQL-@MYSQL_BASE_VERSION@/mysql-%{mysql ...@@ -17,6 +17,7 @@ Source: http://www.mysql.com/Downloads/MySQL-@MYSQL_BASE_VERSION@/mysql-%{mysql
Icon: mysql.gif Icon: mysql.gif
URL: http://www.mysql.com/ URL: http://www.mysql.com/
Packager: David Axmark <david@mysql.com> Packager: David Axmark <david@mysql.com>
Vendor: MySQL AB
Provides: msqlormysql MySQL-server Provides: msqlormysql MySQL-server
Obsoletes: mysql Obsoletes: mysql
...@@ -133,10 +134,10 @@ Summary: MySQL - server with Berkeley DB and Innodb support ...@@ -133,10 +134,10 @@ Summary: MySQL - server with Berkeley DB and Innodb support
Group: Applications/Databases Group: Applications/Databases
Obsoletes: mysql-Max Obsoletes: mysql-Max
%description Max %description Max
Extra MySQL server binary to get support extra features like Optional MySQL server binary that supports features
transactional tables. To active these features on only have to install like transactional tables. To active this binary, just install this
this package after the server package. package after the MySQL package.
%prep %prep
%setup -n mysql-%{mysql_version} %setup -n mysql-%{mysql_version}
......
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