Mysql – GROUP BY two columns

group byMySQLselectupdate

I want to count two columns, but need to get the results of first column in one row.

SELECT country, COUNT(*)
FROM table1
GROUP BY country, type

This query gives me

country    type     COUNT(*)
Canada     first    22
Canada     second   42
Canada     third    15
Australia  second   23
Australia  third    18

but I need to get

country    type_first   type_second   type_third
Canada     22           42            15
Australia  23           18            0

as I want to update another table with these values, and with this row structure, I can update the country table row by row as I get from the above query.

UPDATE country SET first=x, second=x, third=x

NOTE: type column is ENUM with predefined values.

Best Answer

Looks like you want something like:

SELECT country
, sum(case when type = 'first' then 1 else 0 end) as type_first
, sum(case when type = 'second' then 1 else 0 end) as type_second
, sum(case when type = 'third' then 1 else 0 end) as type_third
FROM table1
GROUP BY country

Related Solutions

MySQL unique constraint across two columns

I have modified ypercube's solution a little bit, so that both source and destination are not null, as is guaranteed by the original design. My CHECK constraints are commented out, as they apparently will not work in MySQL. I kept them as comments because they document my intent, and they will work on other RDBMS.

CREATE TABLE PointType
( PointTypeID tinyint unsigned NOT NULL,
  TypeDescription CHAR(20) NOT NULL,
  PRIMARY KEY (PointTypeID),
  UNIQUE (TypeDescription)
) ;

INSERT INTO PointType 
  (PointTypeID, TypeDescription)
VALUES
  (1, 'Source'), 
  (2, 'Destination') ;

CREATE TABLE PointUsageQuota
( RouteID int unsigned NOT NULL,
  PointTypeID tinyint unsigned NOT NULL,
  PointID smallint(5) unsigned NOT NULL,
  PRIMARY KEY (PointID),     -- and this is what all the fuss is about
  UNIQUE (RouteID , PointID, PointTypeID), -- target for the foreign keys
  FOREIGN KEY (PointTypeID)
    REFERENCES PointType (PointTypeID)
) ;

CREATE TABLE Route
( RouteID int unsigned NOT NULL,
  SourcePointID smallint(5) unsigned NOT NULL,
  SourceTypeID tinyint unsigned NOT NULL, 
      -- CHECK(SourceTypeID = 1),
  FOREIGN KEY (RouteID , SourcePointID, SourceTypeID) 
    REFERENCES PointUsageQuota (RouteID , PointID, PointTypeID) ,
  DestinationPointID smallint(5) unsigned NOT NULL,
  DestinationTypeID tinyint unsigned NOT NULL, 
      -- CHECK(DestinationTypeID = 2),
  FOREIGN KEY (RouteID , DestinationPointID, DestinationTypeID) 
    REFERENCES PointUsageQuota (RouteID , PointID, PointTypeID) ,
  --  other fields
  PRIMARY KEY (RouteID)
) ;

Testing:

insert into PointUsageQuota
values(1,1,666),(1,2,354);

INSERT INTO Route VALUES (1, 666, 1, 354, 2);
-- this fails:
INSERT INTO Route VALUES (2, 666, 1, 354, 2);
-- this fails too:
INSERT INTO Route VALUES (2, 354, 1, 666, 2);

Mysql – How to UPDATE MAX and MIN of a GROUP BY

SELECT * FROM test WHERE id IN
(SELECT MIN(id) FROM test GROUP BY category HAVING col='x' 
UNION SELECT MAX(id) FROM test GROUP BY category HAVING col='x')

Fiddle

Best Answer

Related Solutions

MySQL unique constraint across two columns

Mysql – How to UPDATE MAX and MIN of a GROUP BY

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