如何选择表中仅包含所有行的 NULL 值的所有列?我正在使用MS SQL Server 2005。我试图找出表中未使用哪些列,以便删除它们。
15 回答
这是 sql 2005 或更高版本:将 ADDR_Address 替换为您的表名。
declare @col varchar(255), @cmd varchar(max)
DECLARE getinfo cursor for
SELECT c.name FROM sys.tables t JOIN sys.columns c ON t.Object_ID = c.Object_ID
WHERE t.Name = 'ADDR_Address'
OPEN getinfo
FETCH NEXT FROM getinfo into @col
WHILE @@FETCH_STATUS = 0
BEGIN
SELECT @cmd = 'IF NOT EXISTS (SELECT top 1 * FROM ADDR_Address WHERE [' + @col + '] IS NOT NULL) BEGIN print ''' + @col + ''' end'
EXEC(@cmd)
FETCH NEXT FROM getinfo into @col
END
CLOSE getinfo
DEALLOCATE getinfo
SELECT cols
FROM table
WHERE cols IS NULL
这应该为您提供表“Person”中只有 NULL 值的所有列的列表。您将获得多个结果集的结果,这些结果集要么为空,要么包含单个列的名称。您需要在两个地方替换“Person”才能将其与另一个表一起使用。
DECLARE crs CURSOR LOCAL FAST_FORWARD FOR SELECT name FROM syscolumns WHERE id=OBJECT_ID('Person')
OPEN crs
DECLARE @name sysname
FETCH NEXT FROM crs INTO @name
WHILE @@FETCH_STATUS = 0
BEGIN
EXEC('SELECT ''' + @name + ''' WHERE NOT EXISTS (SELECT * FROM Person WHERE ' + @name + ' IS NOT NULL)')
FETCH NEXT FROM crs INTO @name
END
CLOSE crs
DEALLOCATE crs
这是 Bryan 2008 年及以后的查询的更新版本。它使用 INFORMATION_SCHEMA.COLUMNS,为表模式和表名添加变量。列数据类型已添加到输出中。在查找特定数据类型的列时,包括列数据类型会有所帮助。我没有添加列宽或任何东西。
对于输出,使用了 RAISERROR ... WITH NOWAIT,因此文本将立即显示,而不是像 PRINT 那样在最后一次全部显示(大部分情况下)。
SET NOCOUNT ON;
DECLARE
@ColumnName sysname
,@DataType nvarchar(128)
,@cmd nvarchar(max)
,@TableSchema nvarchar(128) = 'dbo'
,@TableName sysname = 'TableName';
DECLARE getinfo CURSOR FOR
SELECT
c.COLUMN_NAME
,c.DATA_TYPE
FROM
INFORMATION_SCHEMA.COLUMNS AS c
WHERE
c.TABLE_SCHEMA = @TableSchema
AND c.TABLE_NAME = @TableName;
OPEN getinfo;
FETCH NEXT FROM getinfo INTO @ColumnName, @DataType;
WHILE @@FETCH_STATUS = 0
BEGIN
SET @cmd = N'IF NOT EXISTS (SELECT * FROM ' + @TableSchema + N'.' + @TableName + N' WHERE [' + @ColumnName + N'] IS NOT NULL) RAISERROR(''' + @ColumnName + N' (' + @DataType + N')'', 0, 0) WITH NOWAIT;';
EXECUTE (@cmd);
FETCH NEXT FROM getinfo INTO @ColumnName, @DataType;
END;
CLOSE getinfo;
DEALLOCATE getinfo;
或者您是否只想查看一列是否只有 NULL 值(因此可能未使用)?
进一步澄清这个问题可能会有所帮助。
编辑: 好的..这里有一些非常粗略的代码可以让你继续......
SET NOCOUNT ON
DECLARE @TableName Varchar(100)
SET @TableName='YourTableName'
CREATE TABLE #NullColumns (ColumnName Varchar(100), OnlyNulls BIT)
INSERT INTO #NullColumns (ColumnName, OnlyNulls) SELECT c.name, 0 FROM syscolumns c INNER JOIN sysobjects o ON c.id = o.id AND o.name = @TableName AND o.xtype = 'U'
DECLARE @DynamicSQL AS Nvarchar(2000)
DECLARE @ColumnName Varchar(100)
DECLARE @RC INT
SELECT TOP 1 @ColumnName = ColumnName FROM #NullColumns WHERE OnlyNulls=0
WHILE @@ROWCOUNT > 0
BEGIN
SET @RC=0
SET @DynamicSQL = 'SELECT TOP 1 1 As HasNonNulls FROM ' + @TableName + ' (nolock) WHERE ''' + @ColumnName + ''' IS NOT NULL'
EXEC sp_executesql @DynamicSQL
set @RC=@@rowcount
IF @RC=1
BEGIN
SET @DynamicSQL = 'UPDATE #NullColumns SET OnlyNulls=1 WHERE ColumnName=''' + @ColumnName + ''''
EXEC sp_executesql @DynamicSQL
END
ELSE
BEGIN
SET @DynamicSQL = 'DELETE FROM #NullColumns WHERE ColumnName=''' + @ColumnName+ ''''
EXEC sp_executesql @DynamicSQL
END
SELECT TOP 1 @ColumnName = ColumnName FROM #NullColumns WHERE OnlyNulls=0
END
SELECT * FROM #NullColumns
DROP TABLE #NullColumns
SET NOCOUNT OFF
是的,有更简单的方法,但我现在要开会。祝你好运!
你可以做:
select
count(<columnName>)
from
<tableName>
如果计数返回 0,则表示该列中的所有行均为 NULL(或表中根本没有行)
可以改为
select
case(count(<columnName>)) when 0 then 'Nulls Only' else 'Some Values' end
from
<tableName>
如果你想自动化它,你可以使用系统表来迭代你感兴趣的表中的列名
如果您需要列出所有列值所在的所有行NULL
,那么我会使用该COLLATE
函数。这需要一个值列表并返回第一个非空值。如果您将所有列名添加到列表中,然后使用IS NULL
,您应该得到所有仅包含空值的行。
SELECT * FROM MyTable WHERE COLLATE(Col1, Col2, Col3, Col4......) IS NULL
您实际上不应该有任何带有 ALLcolumns
空值的表,因为这意味着您没有primary key
(not allowed to be null
)。没有主键是要避免的;这打破了第一范式。
试试这个 -
DECLARE @table VARCHAR(100) = 'dbo.table'
DECLARE @sql NVARCHAR(MAX) = ''
SELECT @sql = @sql + 'IF NOT EXISTS(SELECT 1 FROM ' + @table + ' WHERE ' + c.name + ' IS NOT NULL) PRINT ''' + c.name + ''''
FROM sys.objects o
JOIN sys.columns c ON o.[object_id] = c.[object_id]
WHERE o.[type] = 'U'
AND o.[object_id] = OBJECT_ID(@table)
AND c.is_nullable = 1
EXEC(@sql)
实际上不确定 2005 年,但 2008 年吃了它:
USE [DATABASE_NAME] -- !
GO
DECLARE @SQL NVARCHAR(MAX)
DECLARE @TableName VARCHAR(255)
SET @TableName = 'TABLE_NAME' -- !
SELECT @SQL =
(
SELECT
CHAR(10)
+'DELETE FROM ['+t1.TABLE_CATALOG+'].['+t1.TABLE_SCHEMA+'].['+t1.TABLE_NAME+'] WHERE '
+(
SELECT
CASE t2.ORDINAL_POSITION
WHEN (SELECT MIN(t3.ORDINAL_POSITION) FROM INFORMATION_SCHEMA.COLUMNS t3 WHERE t3.TABLE_NAME=t2.TABLE_NAME) THEN ''
ELSE 'AND '
END
+'['+COLUMN_NAME+'] IS NULL' AS 'data()'
FROM INFORMATION_SCHEMA.COLUMNS t2 WHERE t2.TABLE_NAME=t1.TABLE_NAME FOR XML PATH('')
) AS 'data()'
FROM INFORMATION_SCHEMA.TABLES t1 WHERE t1.TABLE_NAME = @TableName FOR XML PATH('')
)
SELECT @SQL -- EXEC(@SQL)
在这里,我为任何类型的 SQL 表创建了一个脚本。请复制此存储过程并在您的环境中创建它并使用您的表运行此存储过程。
exec [dbo].[SP_RemoveNullValues] 'Your_Table_Name'
存储过程
GO
/****** Object: StoredProcedure [dbo].[SP_RemoveNullValues] Script Date: 09/09/2019 11:26:53 AM ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
-- akila liyanaarachchi
Create procedure [dbo].[SP_RemoveNullValues](@PTableName Varchar(50) ) as
begin
DECLARE Cussor CURSOR FOR
SELECT COLUMN_NAME,TABLE_NAME,DATA_TYPE
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = @PTableName
OPEN Cussor;
Declare @ColumnName Varchar(50)
Declare @TableName Varchar(50)
Declare @DataType Varchar(50)
Declare @Flage int
FETCH NEXT FROM Cussor INTO @ColumnName,@TableName,@DataType
WHILE @@FETCH_STATUS = 0
BEGIN
set @Flage=0
If(@DataType in('bigint','numeric','bit','smallint','decimal','smallmoney','int','tinyint','money','float','real'))
begin
set @Flage=1
end
If(@DataType in('date','atetimeoffset','datetime2','smalldatetime','datetime','time'))
begin
set @Flage=2
end
If(@DataType in('char','varchar','text','nchar','nvarchar','ntext'))
begin
set @Flage=3
end
If(@DataType in('binary','varbinary'))
begin
set @Flage=4
end
DECLARE @SQL VARCHAR(MAX)
if (@Flage in(1,4))
begin
SET @SQL =' update ['+@TableName+'] set ['+@ColumnName+']=0 where ['+@ColumnName+'] is null'
end
if (@Flage =3)
begin
SET @SQL =' update ['+@TableName+'] set ['+@ColumnName+'] = '''' where ['+@ColumnName+'] is null '
end
if (@Flage =2)
begin
SET @SQL =' update ['+@TableName+'] set ['+@ColumnName+'] ='+'''1901-01-01 00:00:00.000'''+' where ['+@ColumnName+'] is null '
end
EXEC(@SQL)
FETCH NEXT FROM Cussor INTO @ColumnName,@TableName,@DataType
END
CLOSE Cussor
DEALLOCATE Cussor
END
您必须遍历这组列并检查每一列。您应该能够使用 DESCRIBE table 命令获取所有列的列表。
伪代码:
foreach $column ($cols) {
query("SELECT count(*) FROM table WHERE $column IS NOT NULL")
if($result is zero) {
# $column contains only null values"
push @onlyNullColumns, $column;
} else {
# $column contains non-null values
}
}
return @onlyNullColumns;
我知道这似乎有点违反直觉,但 SQL 没有提供选择列的本机方法,只有行。
我还建议搜索所有具有相同值的字段,而不仅仅是 NULL。
也就是说,对于每个表中的每一列执行查询:
SELECT COUNT(DISTINCT field) FROM tableName
并专注于结果返回 1 的那些。
SELECT t.column_name
FROM user_tab_columns t
WHERE t.nullable = 'Y' AND t.table_name = 'table name here' AND t.num_distinct = 0;
'user2466387' 版本的更新版本,额外的小测试可以提高性能,因为测试不可为空的列是没有用的:
AND IS_NULLABLE = 'YES'
完整代码:
SET NOCOUNT ON;
DECLARE
@ColumnName sysname
,@DataType nvarchar(128)
,@cmd nvarchar(max)
,@TableSchema nvarchar(128) = 'dbo'
,@TableName sysname = 'TableName';
DECLARE getinfo CURSOR FOR
SELECT
c.COLUMN_NAME
,c.DATA_TYPE
FROM
INFORMATION_SCHEMA.COLUMNS AS c
WHERE
c.TABLE_SCHEMA = @TableSchema
AND c.TABLE_NAME = @TableName
AND IS_NULLABLE = 'YES';
OPEN getinfo;
FETCH NEXT FROM getinfo INTO @ColumnName, @DataType;
WHILE @@FETCH_STATUS = 0
BEGIN
SET @cmd = N'IF NOT EXISTS (SELECT * FROM ' + @TableSchema + N'.' + @TableName + N' WHERE [' + @ColumnName + N'] IS NOT NULL) RAISERROR(''' + @ColumnName + N' (' + @DataType + N')'', 0, 0) WITH NOWAIT;';
EXECUTE (@cmd);
FETCH NEXT FROM getinfo INTO @ColumnName, @DataType;
END;
CLOSE getinfo;
DEALLOCATE getinfo;
你可能需要澄清一下。你真正想要完成什么?如果你真的想找出只包含空值的列名,那么你将不得不遍历架构并基于它进行动态查询。
我不知道您使用的是哪个 DBMS,所以我将在此处放置一些伪代码。
for each col
begin
@cmd = 'if not exists (select * from tablename where ' + col + ' is not null begin print ' + col + ' end'
exec(@cmd)
end