选择列名，其条目是不为空(Select column names whose entries are

我想有至少有一个非表的这些列的列表NULL在其中的数据项。

换句话说，我想获得其下述至少返回一个条目列名：

SELECT DISTINCT column_name FROM table WHERE column_name IS NOT NULL

我试过如下：

SELECT column_name
FROM information_schema.columns
WHERE table_name = "table_name"
AND EXISTS (
    SELECT DISTINCT column_name FROM table_name WHERE column_name IS NOT NULL
)

但是，这也将返回所有的条目列名NULL 。

所以，我怎么只非这些列NULL条目？

Answer 1:

从创建INFORMATION_SCHEMA.COLUMNS表包含要执行的SQL字符串，然后准备语句从串并执行它。

我们要建立将类似于SQL：

  SELECT 'column_a'
  FROM   table_name
  WHERE `column_a` IS NOT NULL
  HAVING COUNT(*)
UNION ALL
  SELECT 'column_b'
  FROM   table_name
  WHERE `column_b` IS NOT NULL
  HAVING COUNT(*)
-- etc.

（人们可以省略WHERE子句和替代COUNT(*)的COUNT(column) ，但我认为这可能是对索引列的低效率）。

这可以通过使用应做到以下几点：

SET group_concat_max_len = 4294967295;

SELECT GROUP_CONCAT(
 ' SELECT ',QUOTE(COLUMN_NAME),
 ' FROM   table_name',
 ' WHERE `',REPLACE(COLUMN_NAME, '`', '``'),'` IS NOT NULL',
 ' HAVING COUNT(*)'
SEPARATOR ' UNION ALL ')
INTO   @sql
FROM   INFORMATION_SCHEMA.COLUMNS
WHERE  TABLE_SCHEMA = DATABASE()
   AND TABLE_NAME = 'table_name';

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

看到它在sqlfiddle 。

Answer 2:

使用此程序会打印列具有ATLEAST一个不空行的表的名称。

create or replace procedure list_col_notNull(tblName in varchar2)
as
lv_col_name varchar2(200);
lv_ctr number;
lv_sql varchar2(400);
CURSOR cur_col_name is
SELECT column_name
FROM USER_TAB_COLUMNS U
WHERE table_name = tblName order by column_name asc;
begin
open cur_col_name;

LOOP
    FETCH cur_col_name INTO lv_col_name; 
    EXIT WHEN cur_col_name%NOTFOUND; 
    lv_sql := 'select count(1) From ' || tblName || ' where ' || lv_col_name || ' is not null'  ;  
    EXECUTE IMMEDIATE lv_sql into lv_ctr;
    if lv_ctr > 0
    then
        dbms_output.put_line(lv_col_name);
    end if;

文章来源: Select column names whose entries are not null