SQL：將許多位/二進制列“轉置”為一個多元列

Question

說我有以下數據：

name  is_married  has_dog  wants_children
Tom            1        1               1
Dick           0        1               1
Harry          0        0               0

但我想產生以下數據：

name  description
Tom   is_married
Tom   has_dog
Tom   wants_children
Dick  has_dog
Dick  wants_children

即，我想將各種二進制字段中保存的信息放入一種形式，其中每個“二進制正數”都顯示在其自己的行中。

如果有成百上千的二進制列，有沒有辦法使它具有可伸縮性？

Answer 1

這是應該擴展的例程。

• 使用INFORMATION_SCHEMA系統表查找列名
• 使用游標遍歷列名
• 遍歷，創建准備/執行以執行特定查詢，以查找具有該屬性的用戶，並將該屬性（列名）轉換為“描述”字段
• 將這些值存儲在臨時表中以進行名稱/描述
• 選擇結果。

例：

DELIMITER $$
CREATE PROCEDURE myproc()
BEGIN  
  DECLARE sql_stmt varchar(200);
  DECLARE exit_loop INTEGER DEFAULT 0;

  DECLARE col_names CURSOR FOR SELECT CONCAT('select name, "', column_name, '" As Description from tbl where ' , column_name, '=1')
  FROM INFORMATION_SCHEMA.COLUMNS
  WHERE table_name = 'tbl'
  and column_name <> 'Name'
  ORDER BY ordinal_position;

  DECLARE CONTINUE HANDLER FOR NOT FOUND SET exit_loop = TRUE;

CREATE TEMPORARY TABLE temp (name varchar(200), description varchar(200));

OPEN col_names;

the_loop: LOOP

   FETCH col_names 
   INTO sql_stmt; 

   IF exit_loop THEN
        CLOSE col_names;
        LEAVE the_loop;
   END IF;

SET @s = CONCAT('INSERT INTO temp(name, description) ',sql_stmt);


PREPARE stmt1 FROM @s;
EXECUTE stmt1;

END LOOP the_loop;

SELECT * from temp ORDER BY name;

DROP TABLE temp;

END$$
DELIMITER ;

結果：

mysql> call myproc();
+------+----------------+
| name | description    |
+------+----------------+
| Tom  | ismarried      |
| Tom  | hasdog         |
| Tom  | wants_children |
| Dick | hasdog         |
| Dick | wants_children |
+------+----------------+
5 rows in set (0.00 sec)