4

以下のようなテーブルがあります

CREATE TABLE Statistics(Stat_Id INT NOT NULL PRIMARY KEY AUTO_INCREMENT,
                        Period  VARCHAR(55),
                        Location VARCHAR(255),
                        Rate_per_SqFt INT)

表のデータは次のとおりです。

INSERT INTO Statistics(Period, Location, Rate_per_SqFt)
                VALUES('June', 'Location A', 2500),
                      ('June', 'Location B', 2740),
                      ('June', 'Location C', 3200),
                      ('July', 'Location A', 2650),
                      ('July', 'Location B', 2800),
                      ('July', 'Location C', 3250),
                      ('August', 'Location A', 2750),
                      ('August', 'Location B', 2950),
                      ('August', 'Location C', 3230),
                      ('October', 'Location A', 2950),
                      ('October', 'Location B', 3950),
                      ('October', 'Location C', 3530);

以下のように、特定の月の行を個別の列として出力に表示したい

 Period   Location A     Location B     Location C 
 June        2500          2740           3200
 July        2650          2800           3250
 August      2750          2950           3230
 October     2950          3950           3530

クエリを使用してこれを行うにはどうすればよいですか

4

1 に答える 1

4 
SELECT Period,
        MAX(CASE WHEN Location = 'Location A' THEN Rate_per_SqFt ELSE NULL END) `Location A`,
        MAX(CASE WHEN Location = 'Location B' THEN Rate_per_SqFt ELSE NULL END) `Location B`,
        MAX(CASE WHEN Location = 'Location C' THEN Rate_per_SqFt ELSE NULL END) `Location C`
FROM statistics
GROUP BY Period

場所の数が不明な場合は、動的 SQL が推奨されます

SET @sql = NULL;
SELECT
  GROUP_CONCAT(DISTINCT
    CONCAT(
      'MAX(CASE WHEN Location = ''',
      Location,
      ''' then Rate_per_SqFt ELSE NULL end) AS ',
      CONCAT('`',Location,'`')
    )
  ) INTO @sql
FROM statistics;

SET @sql = CONCAT('SELECT Period, ', @sql, ' 
                   FROM Statistics 
                   GROUP BY Period');

PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
于 2012-12-29T07:12:54.257 に答える