如何在PHP中按年份计算一栏中的项目数

Question

Is this possible? I have the following table

ID   CAR  MODEL  YEAR   FUELTYPE
1    Volvo S80   2007        GAS
2    Volvo S80D  2007        DIESEL
3    Volvo S80E  2009        LPN

What I want to do is to count the different FUELTYPE's by year, the output would be something like this, this is the format for the Google Chart I want to use.

Year GAS DIESEL LPN
2007  1     1    0
2009  0     0    1

How can I do it with MySQL? Can I do something like this?

SELECT YEAR, COUNT(FUELTYPE) AS GAS, COUNT (FUELTYPE) AS DIESEL, COUNT (FUELTYPE) AS LPN
FROM  CARDATA
GROUP BY FUELTYPE
ORDER BY YEAR

I know it is not right as I get the same count value in each FUELTYPE - is it better to just pull it out of mysql and then use php to sort/count?

Answer 1

You can use an aggregate function with a CASE expression to pivot the row data into columns:

select year,
  sum(case when fueltype = 'gas' then 1 else 0 end) gas,
  sum(case when fueltype = 'diesel' then 1 else 0 end) diesel,
  sum(case when fueltype = 'lpn' then 1 else 0 end) lpn
from yt
group by year

See SQL Fiddle with Demo .

If you have an unknown number of FuelType values, then you can use a prepared statement to generate dynamic SQL:

SET @sql = NULL;
SELECT
  GROUP_CONCAT(DISTINCT
    CONCAT(
      'sum(CASE WHEN fueltype = ''',
      fueltype,
      ''' THEN 1 else 0 END) AS `',
      fueltype, '`'
    )
  ) INTO @sql
FROM yt;

SET @sql 
  = CONCAT('SELECT year, ', @sql, ' 
            from yt
            group by year');

PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

See SQL Fiddle with Demo . Both this the result:

| YEAR | GAS | DIESEL | LPN |
-----------------------------
| 2007 |   1 |      1 |   0 |
| 2009 |   0 |      0 |   1 |

Answer 2

If there are only three FuelType , the easiest solution on this in MySQL is by using GROUP BY , and SUM() .

SELECT  Year,
        SUM(FUELTYPE = 'GAS') GAS,
        SUM(FUELTYPE = 'DIESEL') DIESEL,
        SUM(FUELTYPE = 'LPN') LPN
FROM    CARDATA
GROUP   BY YEAR

• SQLFiddle Demo

but if you have unknown number of FUELTYPE , a dynamic sql is more prefereed.

SET @sql = NULL;

SELECT  GROUP_CONCAT(DISTINCT
        CONCAT('SUM(FUELTYPE = ''',
               FUELTYPE, ''') AS ',
               CONCAT('`', FUELTYPE, '`')
               )) INTO @sql
FROM CARDATA;

SET @sql = CONCAT('SELECT   Year, ', @sql, ' 
                   FROM CARDATA
                   GROUP BY YEAR');

PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

• SQLFiddle Demo

OUTPUT

╔══════╦═════╦════════╦═════╗
║ YEAR ║ GAS ║ DIESEL ║ LPN ║
╠══════╬═════╬════════╬═════╣
║ 2007 ║   1 ║      1 ║   0 ║
║ 2009 ║   0 ║      0 ║   1 ║
╚══════╩═════╩════════╩═════╝