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Tutorial on principles and applications of database system (052) -- data integrity of MySQL (XIV): crosstab query (row column conversion)
2022-07-24 00:51:00 【Rsda DBA_ WGX】
Database system principle and Application Tutorial （052）—— MySQL Data integrity （ fourteen ）： Crosstab query （ Row column conversion ）
Catalog
Crosstab query is to group the columns in the table , A set of columns is on the left side of the crosstab , A group is listed at the top of the crosstab , Various calculated values of a field in the table are displayed at the intersection of rows and columns in the cross table .
Crosstab is divided into static crosstab and dynamic crosstab . The columns in the static crosstab are fixed , Moreover, the data content in the column to be converted into row and column should be determined in advance , Insufficient flexibility in use . The columns in the dynamic crosstab are dynamically generated according to the data in the columns to be converted into rows and columns , There is no need to determine the data content of this column in advance , You don't even need to know what the data in this column is .
Use crosstab queries to calculate and reconstruct data , It can simplify data analysis . Crosstab query calculates the sum of data , Average , Counting and other types of Statistics , And group them , A set of columns are on the left side of the data table as row fields of the crosstab , Another group of columns is at the top of the data table as the column fields of the crosstab .
One 、 In the form of a crosstab
Crosstab query is also called row column conversion , Is to convert the following query results into tables 1（ Crossover table ）.
/* select s.s_id, s.s_name, c.c_id, c.c_name, sc.score from student s,course c,score sc where s.s_id=sc.s_id and c.c_id=sc.c_id; */
mysql> select s.s_id, s.s_name, c.c_id, c.c_name, sc.score
-> from student s,course c,score sc where s.s_id=sc.s_id and c.c_id=sc.c_id;
+-------+-----------+------+--------------+-------+
| s_id | s_name | c_id | c_name | score |
+-------+-----------+------+--------------+-------+
| S2011 | Zhang Xiaogang | C102 | Advanced mathematics | 84 |
| S2011 | Zhang Xiaogang | C105 | Infectious diseases | 90 |
| S2012 | Liu Xiaoqing | C101 | Ancient literature | 67 |
| S2012 | Liu Xiaoqing | C102 | Advanced mathematics | 52 |
| S2012 | Liu Xiaoqing | C103 | linear algebra | 55 |
| S2012 | Liu Xiaoqing | C104 | Clinical medicine | 86 |
| S2012 | Liu Xiaoqing | C105 | Infectious diseases | 87 |
| S2013 | Cao mengde | C102 | Advanced mathematics | 97 |
| S2013 | Cao mengde | C103 | linear algebra | 68 |
| S2013 | Cao mengde | C104 | Clinical medicine | 66 |
| S2013 | Cao mengde | C105 | Infectious diseases | 68 |
| S2014 | Liu Yan | C102 | Advanced mathematics | 90 |
| S2014 | Liu Yan | C103 | linear algebra | 85 |
| S2014 | Liu Yan | C104 | Clinical medicine | 77 |
| S2014 | Liu Yan | C105 | Infectious diseases | 96 |
| S2015 | Liu Yan | C101 | Ancient literature | 69 |
| S2015 | Liu Yan | C102 | Advanced mathematics | 66 |
| S2015 | Liu Yan | C103 | linear algebra | 88 |
| S2015 | Liu Yan | C104 | Clinical medicine | 69 |
| S2015 | Liu Yan | C105 | Infectious diseases | 66 |
| S2016 | Liu Ruofei | C101 | Ancient literature | 65 |
| S2016 | Liu Ruofei | C102 | Advanced mathematics | 69 |
| S2021 | Dong Wenhua | C102 | Advanced mathematics | 72 |
| S2021 | Dong Wenhua | C103 | linear algebra | 90 |
| S2021 | Dong Wenhua | C104 | Clinical medicine | 90 |
| S2021 | Dong Wenhua | C105 | Infectious diseases | 57 |
| S2022 | Zhou Huajian | C102 | Advanced mathematics | 88 |
| S2022 | Zhou Huajian | C103 | linear algebra | 93 |
| S2023 | trump | C102 | Advanced mathematics | 68 |
| S2023 | trump | C103 | linear algebra | 86 |
| S2024 | Obama | C102 | Advanced mathematics | 87 |
| S2024 | Obama | C103 | linear algebra | 97 |
| S2025 | Zhou Jianhua | C102 | Advanced mathematics | 61 |
| S2025 | Zhou Jianhua | C105 | Infectious diseases | 62 |
| S2026 | Zhang Xueyou | C102 | Advanced mathematics | 59 |
| S2026 | Zhang Xueyou | C105 | Infectious diseases | 48 |
+-------+-----------+------+--------------+-------+
36 rows in set (0.00 sec)
-- surface 1（ Crossover table ）
+-----------+------------+------------+------------+-------------+-------------+--------+
| s_name | Ancient literature | Advanced mathematics | linear algebra | Clinical medicine | Infectious diseases | Total score |
+-----------+------------+------------+------------+-------------+-------------+--------+
| Liu Xiaoqing | 67 | 52 | 55 | 86 | 87 | 347 |
| Liu Yan | 69 | 156 | 173 | 146 | 16 | 706 |
| Liu Ruofei | 65 | 69 | Not elective | Not elective | Not elective | 134 |
| Zhou Jianhua | Not elective | 61 | Not elective | Not elective | 62 | 123 |
| Zhou Huajian | Not elective | 88 | 93 | Not elective | Not elective | 181 |
| Obama | Not elective | 87 | 97 | Not elective | Not elective | 184 |
| Zhang Xueyou | Not elective | 59 | Not elective | Not elective | 48 | 107 |
| Zhang Xiaogang | Not elective | 84 | Not elective | Not elective | 90 | 174 |
| Cao mengde | Not elective | 97 | 68 | 66 | 68 | 299 |
| trump | Not elective | 68 | 86 | Not elective | Not elective | 154 |
| Dong Wenhua | Not elective | 72 | 90 | 90 | 57 | 309 |
+-----------+-------------+-----------+-------------+-------------+-------------+--------+
Two 、 Static crosstab
The basic method of generating crosstab is ：
（1） Group according to the row fields of the crosstab （ such as s_name）.
（2） For row fields to be converted to columns （ such as c_name） Make statistics , Use in statistical functions IF Function to filter the data , Generate column fields .
The cross table query code is as follows ：
/* select ifnull(s_name,' Total score ') full name , if(sum(if(c.c_id='C101',score,0))=0,' Not elective ',sum(if(c.c_id='C101',score,0))) Ancient literature , if(sum(if(c.c_id='C102',score,0))=0,' Not elective ',sum(if(c.c_id='C102',score,0))) Advanced mathematics , if(sum(if(c.c_id='C103',score,0))=0,' Not elective ',sum(if(c.c_id='C103',score,0))) linear algebra , if(sum(if(c.c_id='C104',score,0))=0,' Not elective ',sum(if(c.c_id='C104',score,0))) Clinical medicine , if(sum(if(c.c_id='C105',score,0))=0,' Not elective ',sum(if(c.c_id='C105',score,0))) Infectious diseases , sum(score) Total score from student s,course c,score sc where s.s_id=sc.s_id and c.c_id=sc.c_id group by s_name with rollup; */
mysql> select ifnull(s_name,' Total score ') full name ,
-> if(sum(if(c.c_id='C101',score,0))=0,' Not elective ',sum(if(c.c_id='C101',score,0))) Ancient literature ,
-> if(sum(if(c.c_id='C102',score,0))=0,' Not elective ',sum(if(c.c_id='C102',score,0))) Advanced mathematics ,
-> if(sum(if(c.c_id='C103',score,0))=0,' Not elective ',sum(if(c.c_id='C103',score,0))) linear algebra ,
-> if(sum(if(c.c_id='C104',score,0))=0,' Not elective ',sum(if(c.c_id='C104',score,0))) Clinical medicine ,
-> if(sum(if(c.c_id='C105',score,0))=0,' Not elective ',sum(if(c.c_id='C105',score,0))) Infectious diseases ,
-> sum(score) Total score
-> from student s,course c,score sc where s.s_id=sc.s_id and c.c_id=sc.c_id
-> group by s_name with rollup;
+-----------+-------------+-------------+-------------+-------------+-------------+--------+
| full name | Ancient literature | Advanced mathematics | linear algebra | Clinical medicine | Infectious diseases | Total score |
+-----------+-------------+-------------+-------------+-------------+-------------+--------+
| Liu Xiaoqing | 67 | 52 | 55 | 86 | 87 | 347 |
| Liu Yan | 69 | 156 | 173 | 146 | 162 | 706 |
| Liu Ruofei | 65 | 69 | Not elective | Not elective | Not elective | 134 |
| Zhou Jianhua | Not elective | 61 | Not elective | Not elective | 62 | 123 |
| Zhou Huajian | Not elective | 88 | 93 | Not elective | Not elective | 181 |
| Obama | Not elective | 87 | 97 | Not elective | Not elective | 184 |
| Zhang Xueyou | Not elective | 59 | Not elective | Not elective | 48 | 107 |
| Zhang Xiaogang | Not elective | 84 | Not elective | Not elective | 90 | 174 |
| Cao mengde | Not elective | 97 | 68 | 66 | 68 | 299 |
| trump | Not elective | 68 | 86 | Not elective | Not elective | 154 |
| Dong Wenhua | Not elective | 72 | 90 | 90 | 57 | 309 |
| Total score | 201 | 893 | 662 | 388 | 574 | 2718 |
+-----------+--------------+-------------+-------------+-------------+-------------+--------+
12 rows in set (0.03 sec)
3、 ... and 、 Dynamic crosstab
The basic idea of realizing dynamic crosstab is ：
（1） Use GROUP_CONCAT The function retrieves all the data in the column to be row column conversion .
（2） Use CONCAT Functions are spliced into the same as static crosstab queries SELECT sentence .
（3） Use pretreatment （prepare） Command execution , Get the final query result .
Still with the above student、course、score Take three tables as an example , Dynamically generate crosstab .
1、 Take out the data in the column to be row column conversion
Use GROUP_CONCAT Function to get the column to be converted into row and column （c_name） Data in .
/* select group_concat(distinct c.c_name) from student s,course c,score sc where s.s_id=sc.s_id and c.c_id=sc.c_id; */
mysql> select group_concat(distinct c.c_name)
-> from student s,course c,score sc where s.s_id=sc.s_id and c.c_id=sc.c_id;
+------------------------------------------------------------------+
| group_concat(distinct c.c_name) |
+------------------------------------------------------------------+
| Clinical medicine , Infectious diseases , Ancient literature , linear algebra , Advanced mathematics |
+------------------------------------------------------------------+
1 row in set (0.00 sec)
2、 Use CONCAT Function to generate a concatenated string
/* explain ： by \' For escape characters , Put single quotation marks （'） Splice into string SELECT GROUP_CONCAT(DISTINCT (CONCAT('IF(SUM(IF(c_name=\'',c_name,'\',score,0))=0,\' Not elective \',SUM(IF(c_name=\'',c_name,'\',score,0))) ',c_name)) ) INTO @sql_str FROM student s,course c,score sc, (SELECT @sql_str) a where s.s_id=sc.s_id and c.c_id=sc.c_id; */
mysql> SELECT GROUP_CONCAT(DISTINCT
-> (CONCAT('IF(SUM(IF(c_name=\'',c_name,'\',score,0))=0,\' Not elective \',SUM(IF(c_name=\'',c_name,'\',score,0))) ',c_name))
-> )
-> INTO @sql_str
-> FROM student s,course c,score sc, (SELECT @sql_str) a
-> where s.s_id=sc.s_id and c.c_id=sc.c_id;
Query OK, 1 row affected (0.00 sec)
mysql> SELECT @sql_str;
+-----------------------------------------------------------+|
@sql_str
|+----------------------------------------------------------+|
IF(SUM(IF(c_name=' Clinical medicine ',score,0))=0,' Not elective ',SUM(IF(c_name=' Clinical medicine ',score,0))) Clinical medicine ,
IF(SUM(IF(c_name=' Infectious diseases ',score,0))=0,' Not elective ',SUM(IF(c_name=' Infectious diseases ',score,0))) Infectious diseases ,
IF(SUM(IF(c_name=' Ancient literature ',score,0))=0,' Not elective ',SUM(IF(c_name=' Ancient literature ',score,0))) Ancient literature ,
IF(SUM(IF(c_name=' linear algebra ',score,0))=0,' Not elective ',SUM(IF(c_name=' linear algebra ',score,0))) linear algebra ,
IF(SUM(IF(c_name=' Advanced mathematics ',score,0))=0,' Not elective ',SUM(IF(c_name=' Advanced mathematics ',score,0))) Advanced mathematics
|+-------------------------------------------------------------------------+
1 row in set (0.00 sec)
3、 A complete mosaic SELECT sentence
/* SELECT GROUP_CONCAT(DISTINCT (CONCAT('IF(SUM(IF(c_name=\'',c_name,'\',score,0))=0,\' Not elective \',SUM(IF(c_name=\'',c_name,'\',score,0))) ',c_name)) ) INTO @sql_str FROM student s,course c,score sc, (SELECT @sql_str) a where s.s_id=sc.s_id and c.c_id=sc.c_id; set @sql_str = CONCAT('SELECT IFNULL(s_name, \' Total score \') full name ,', @sql_str, ',SUM(score) Total score FROM student s,course c,score sc where s.s_id=sc.s_id and c.c_id=sc.c_id GROUP BY s.s_name WITH ROLLUP;'); */
mysql> SELECT GROUP_CONCAT(DISTINCT
-> (CONCAT('IF(SUM(IF(c_name=\'',c_name,'\',score,0))=0,\' Not elective \',SUM(IF(c_name=\'',c_name,'\',score,0))) ',c_name))
-> )
-> INTO @sql_str
-> FROM student s,course c,score sc, (SELECT @sql_str) a
-> where s.s_id=sc.s_id and c.c_id=sc.c_id;
Query OK, 1 row affected (0.00 sec)
mysql> set @sql_str =
-> CONCAT('SELECT IFNULL(s_name, \' Total score \') full name ,',
-> @sql_str,
-> ',SUM(score) Total score '> FROM student s,course c,score sc
'> where s.s_id=sc.s_id and c.c_id=sc.c_id '> GROUP BY s.s_name WITH ROLLUP;'); Query OK, 0 rows affected (0.00 sec)'
mysql> select @sql_str;
+---------------------------------------------------------------+|
@sql_str
|+-------------------------------------------------------------+|
SELECT
IFNULL(s_name, ' Total score ') full name ,
IF(SUM(IF(c_name=' Clinical medicine ',score,0))=0,' Not elective ',SUM(IF(c_name=' Clinical medicine ',score,0))) Clinical medicine ,
IF(SUM(IF(c_name=' Infectious diseases ',score,0))=0,' Not elective ',SUM(IF(c_name=' Infectious diseases ',score,0))) Infectious diseases ,
IF(SUM(IF(c_name=' Ancient literature ',score,0))=0,' Not elective ',SUM(IF(c_name=' Ancient literature ',score,0))) Ancient literature ,
IF(SUM(IF(c_name=' linear algebra ',score,0))=0,' Not elective ',SUM(IF(c_name=' linear algebra ',score,0))) linear algebra ,
IF(SUM(IF(c_name=' Advanced mathematics ',score,0))=0,' Not elective ',SUM(IF(c_name=' Advanced mathematics ',score,0))) Advanced mathematics ,
SUM(score) Total score
FROM student s,course c,score sc
where s.s_id=sc.s_id and c.c_id=sc.c_id
GROUP BY s.s_name WITH ROLLUP;
+---------------------------------------------------------------------------+
1 row in set (0.00 sec)
4、 Use the preprocessing command to execute the spliced string
/* -- PREPARE Statement syntax description ： PREPARE statement_name FROM SQL character string ; -- Execute preprocessing statements EXECUTE statement_name; -- Delete the preprocessing statement definition DEALLOCATE | DROP PREPARE statement_name; */
mysql> PREPARE stmt from @sql_str;
Query OK, 0 rows affected (0.00 sec)
Statement prepared
mysql> EXECUTE stmt;
+-----------+-------------+-------------+-------------+--------------+-------------+--------+
| full name | Clinical medicine | Infectious diseases | Ancient literature | linear algebra | Advanced mathematics | Total score |
+-----------+-------------+-------------+-------------+--------------+-------------+--------+
| Liu Xiaoqing | 86 | 87 | 67 | 55 | 52 | 347 |
| Liu Yan | 146 | 162 | 69 | 173 | 156 | 706 |
| Liu Ruofei | Not elective | Not elective | 65 | Not elective | 69 | 134 |
| Zhou Jianhua | Not elective | 62 | Not elective | Not elective | 61 | 123 |
| Zhou Huajian | Not elective | Not elective | Not elective | 93 | 88 | 181 |
| Obama | Not elective | Not elective | Not elective | 97 | 87 | 184 |
| Zhang Xueyou | Not elective | 48 | Not elective | Not elective | 59 | 107 |
| Zhang Xiaogang | Not elective | 90 | Not elective | Not elective | 84 | 174 |
| Cao mengde | 66 | 68 | Not elective | 68 | 97 | 299 |
| trump | Not elective | Not elective | Not elective | 86 | 68 | 154 |
| Dong Wenhua | 90 | 57 | Not elective | 90 | 72 | 309 |
| Total score | 388 | 574 | 201 | 662 | 893 | 2718 |
+-----------+-------------+--------------+-------------+--------------+-------------+--------+
12 rows in set (0.00 sec)
mysql> DEALLOCATE prepare stmt;
Query OK, 0 rows affected (0.00 sec)
5、 Define the crosstab query as a stored procedure
Define the above code as a stored procedure stored in the database , Call repeatedly .
The code is as follows ：
DELIMITER &&
CREATE PROCEDURE sp_crosstable() reads SQL data
BEGIN
SET @sql_str = NULL;
SELECT GROUP_CONCAT(DISTINCT
(CONCAT('IF(SUM(IF(c_name=\'',c_name,'\',score,0))=0,\' Not elective \',SUM(IF(c_name=\'',c_name,'\',score,0))) ',c_name))
)
INTO @sql_str
FROM student s,course c,score sc, (SELECT @sql_str) a
where s.s_id=sc.s_id and c.c_id=sc.c_id;
set @sql_str =
CONCAT('SELECT IFNULL(s_name, \' Total score \') full name ,',
@sql_str,
',SUM(score) Total score FROM student s,course c,score sc where s.s_id=sc.s_id and c.c_id=sc.c_id GROUP BY s.s_name WITH ROLLUP;');
PREPARE stmt from @sql_str;
EXECUTE stmt;
DEALLOCATE prepare stmt;
END &&
DELIMITER ;
Execute the above code , Generate stored procedure ：
mysql> DELIMITER &&
mysql> CREATE PROCEDURE sp_crosstable() reads SQL data
-> BEGIN
-> SET @sql_str = NULL;
->
-> SELECT GROUP_CONCAT(DISTINCT
-> (CONCAT('IF(SUM(IF(c_name=\'',c_name,'\',score,0))=0,\' Not elective \',SUM(IF(c_name=\'',c_name,'\',score,0))) ',c_name))
-> )
-> INTO @sql_str
-> FROM student s,course c,score sc, (SELECT @sql_str) a
-> where s.s_id=sc.s_id and c.c_id=sc.c_id;
->
-> set @sql_str =
-> CONCAT('SELECT IFNULL(s_name, \' Total score \') full name ,',
-> @sql_str,
-> ',SUM(score) Total score '> FROM student s,course c,score sc
'> where s.s_id=sc.s_id and c.c_id=sc.c_id '> GROUP BY s.s_name WITH ROLLUP;'); -> -> PREPARE stmt from @sql_str; -> EXECUTE stmt; -> DEALLOCATE prepare stmt; -> END && Query OK, 0 rows affected (0.10 sec) mysql> DELIMITER ; mysql> select name from mysql.proc where db='mydb';
+---------------+
| name |
+---------------+
| sp_crosstable |
+---------------+
1 row in set (0.01 sec)
Execute stored procedures , Generate crosstab ：
mysql> CALL sp_crosstable;
+-----------+--------------+--------------+--------------+--------------+--------------+--------+
| full name | Clinical medicine | Infectious diseases | Ancient literature | linear algebra | Advanced mathematics | Total score |
+-----------+--------------+--------------+--------------+--------------+--------------+--------+
| Liu Xiaoqing | 86 | 87 | 67 | 55 | 52 | 347 |
| Liu Yan | 146 | 162 | 69 | 173 | 156 | 706 |
| Liu Ruofei | Not elective | Not elective | 65 | Not elective | 69 | 134 |
| Zhou Jianhua | Not elective | 62 | Not elective | Not elective | 61 | 123 |
| Zhou Huajian | Not elective | Not elective | Not elective | 93 | 88 | 181 |
| Obama | Not elective | Not elective | Not elective | 97 | 87 | 184 |
| Zhang Xueyou | Not elective | 48 | Not elective | Not elective | 59 | 107 |
| Zhang Xiaogang | Not elective | 90 | Not elective | Not elective | 84 | 174 |
| Cao mengde | 66 | 68 | Not elective | 68 | 97 | 299 |
| trump | Not elective | Not elective | Not elective | 86 | 68 | 154 |
| Dong Wenhua | 90 | 57 | Not elective | 90 | 72 | 309 |
| Total score | 388 | 574 | 201 | 662 | 893 | 2718 |
+-----------+--------------+--------------+--------------+--------------+--------------+--------+
12 rows in set (0.03 sec)
Query OK, 0 rows affected (0.03 sec)
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