mysql - 从表中仅选择具有空值/空值的列

Question

我有一个看起来像这样的数据集，但列继续为 data4、data5 到 data20

id      data1       data2       data3
(int)   (varchar)   (int)       (date)
-------------------------------------
1       xyz         (null)      0000-00-00
2       (empty)     321         2013-09-02
3       abc         555         2013-02-29
4       def         (null)      2013-09-02
5       lmn         678         2013-03-19

我只想选择包含空值或空值的列的行，以便客户可以决定哪些字段需要填写在他们的工单中。

data1       data2       data3
(varchar)   (int)       (date)
-------------------------------------
2            1,4          1,5

或者如果有人能想到更好的变体？我现在对任何事情都持开放态度，只要它在做我想要的工作。这可能吗？谢谢!

Answer 1

你可以像这样用动态 SQL 来做

DELIMITER $$
CREATE PROCEDURE sp_empty()
BEGIN
  SET @sql = NULL;

  SELECT GROUP_CONCAT(
           CONCAT('(SELECT GROUP_CONCAT(id) FROM Table1 WHERE `', 
                  column_name, '` IS NULL ',
                  CASE  
                    WHEN data_type IN('varchar', 'char') 
                      THEN CONCAT('OR `', column_name, '` = ''''')
                    WHEN data_type IN('date', 'datetime', 'time') 
                      THEN CONCAT('OR `', column_name, '` = 0')
                    ELSE ''
                  END, ')`', column_name, '`'))
     INTO @sql
    FROM INFORMATION_SCHEMA.COLUMNS
   WHERE table_schema = SCHEMA()
     AND table_name = 'table1'
     AND column_name NOT IN ('id')
   GROUP BY table_name;

  SET @sql = CONCAT('SELECT ', @sql);

  PREPARE stmt FROM @sql;
  EXECUTE stmt;
  DEALLOCATE PREPARE stmt;
END$$
DELIMITER ;

请注意，它会处理不同数据类型的列。

示例用法:

CALL sp_empty();

输出:

| DATA1 | DATA2 | DATA3 ||-------|-------|-------||     2 |   1,4 |     1 |

Here is SQLFiddle demo

---

You obviously don't necessarily have to use a stored procedure. It's just simplifies things on the calling end. You can do

SET @sql = NULL;

SELECT GROUP_CONCAT(
         CONCAT('(SELECT GROUP_CONCAT(id) FROM Table1 WHERE `', 
                column_name, '` IS NULL ',
                CASE  
                  WHEN data_type IN('varchar', 'char') 
                    THEN CONCAT('OR `', column_name, '` = ''''')
                  WHEN data_type IN('date', 'datetime', 'time') 
                    THEN CONCAT('OR `', column_name, '` = 0')
                  ELSE ''
                END, ')`', column_name, '`'))
   INTO @sql
  FROM INFORMATION_SCHEMA.COLUMNS
 WHERE table_schema = SCHEMA()
   AND table_name = 'table1'
   AND column_name NOT IN ('id')
 GROUP BY table_name;

SET @sql = CONCAT('SELECT ', @sql);

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

这是 SQLFiddle 演示

---

如果出于某种原因您不能使用带有动态 SQL 的版本，那么作为最后的手段，您可以自己生成这样的查询，包括您的所有列

SELECT 
(
  SELECT GROUP_CONCAT(id) 
     FROM Table1 
    WHERE `data1` IS NULL 
       OR `data1` = ''
) `data1`,
(
  SELECT GROUP_CONCAT(id) 
    FROM Table1 
   WHERE `data2` IS NULL
) `data2`,
(
  SELECT GROUP_CONCAT(id) 
    FROM Table1 
   WHERE `data3` IS NULL 
      OR `data3` = 0
) `data3`
...

这是 SQLFiddle 演示