我有一个smalldatetime列,我需要将其更改为datetime列。这是安装过程的一部分,因此它不能是手动过程。不幸的是,该列有一些索引和一个非空约束。索引与性能相关,只需使用新数据类型即可保留。是否有可能编写一个语句,允许我在更改列数据类型的同时保留相关信息?如果是这样,怎么办呢?
答案 0 :(得分:12)
您无法使用索引,唯一约束,外键约束或检查约束将数据类型从smalldatetime更改为datetime。在更改类型之前,您必须将它们全部丢弃。然后:
alter table T alter column TestDate datetime not null
然后重新创建仍然适用的约束和索引。
生成drop的一些不同方法并创建:
1)如果您已为所有索引和约束指定了明确的名称,那么您的安装程序可以在每个环境中运行静态脚本(开发,测试,用户验收测试,性能测试等,生产。)
要生成此显式脚本,您可以: a)使用SSMS(或SQL Server 2000,企业管理器)编写create和drop语句的脚本。 b)从您的源代码存储库开始工作,以发现依赖对象的名称和定义,并将相应的静态脚本放在一起。 c)尝试运行alter语句。看看它失败了。查找定义并手写drop和create。 (就个人而言,这对于编写drop而言非常有用,但在创建时并不是很好。)
2)如果您没有为所有索引和约束指定明确的名称,那么安装程序必须在数据字典中查询相应的名称,并使用动态SQL以正确的顺序运行drop,然后再进行更改列语句,然后在更改列之后以正确的顺序创建。
如果您知道没有约束,只有索引,这将更简单。
可能有工具或库已经知道如何执行此操作。
此外,如果这是打包的应用程序,您可能无法确保本地DBA没有添加索引。
注意:如果存在唯一约束,它将构建一个索引,您将无法使用DROP INDEX删除该索引。
答案 1 :(得分:7)
如果您只是更改尺寸,索引仍将保留在桌面上。
如果要更改数据类型,则会收到一条错误消息,指出对象依赖于您尝试更改的列,因此您将无法更改它。
您可以手动或通过脚本编写有问题的索引。在SSMS中,右键单击该表并编写相关对象的脚本。
如果你想要编程索引脚本,这里是我一直使用的存储过程,我是从我的一位前同事那里得到的。
Drop Proc ScriptIndex
GO
Create Proc ScriptIndex
@TableName VarChar (Max),
@IndexScript VarChar (Max) OUTPUT
AS
-- Get all existing indexes, EXCEPT the primary keys
DECLARE cIX CURSOR FOR
SELECT OBJECT_NAME(SI.Object_ID), SI.Object_ID, SI.Name, SI.Index_ID
FROM Sys.Indexes SI
LEFT JOIN INFORMATION_SCHEMA.TABLE_CONSTRAINTS TC
ON SI.Name = TC.CONSTRAINT_NAME
AND OBJECT_NAME(SI.Object_ID) = TC.TABLE_NAME
WHERE 1=1
AND OBJECT_NAME(SI.Object_ID) = @TableName
AND TC.CONSTRAINT_NAME IS NULL
AND OBJECTPROPERTY(SI.Object_ID, 'IsUserTable') = 1
ORDER BY OBJECT_NAME(SI.Object_ID), SI.Index_ID
DECLARE @IxTable SYSNAME
DECLARE @IxTableID INT
DECLARE @IxName SYSNAME
DECLARE @IxID INT
-- Loop through all indexes
OPEN cIX
FETCH NEXT FROM cIX INTO @IxTable, @IxTableID, @IxName, @IxID
WHILE (@@FETCH_STATUS = 0)
BEGIN
DECLARE @IXSQL NVARCHAR(4000)
DECLARE @PKSQL NVARCHAR(4000)
SET @PKSQL = ''
SET @IXSQL = 'CREATE '
-- Check if the index is unique
IF (INDEXPROPERTY(@IxTableID, @IxName, 'IsUnique') = 1)
SET @IXSQL = @IXSQL + 'UNIQUE '
-- Check if the index is clustered
IF (INDEXPROPERTY(@IxTableID, @IxName, 'IsClustered') = 1)
SET @IXSQL = @IXSQL + 'CLUSTERED '
SET @IXSQL = @IXSQL + 'INDEX ' + @IxName + ' ON ' + @IxTable + '('
-- Get all columns of the index
DECLARE cIxColumn CURSOR FOR
SELECT SC.Name
FROM Sys.Index_Columns IC
JOIN Sys.Columns SC ON IC.Object_ID = SC.Object_ID AND IC.Column_ID = SC.Column_ID
WHERE IC.Object_ID = @IxTableID AND Index_ID = @IxID
ORDER BY IC.Index_Column_ID
DECLARE @IxColumn SYSNAME
DECLARE @IxFirstColumn BIT SET @IxFirstColumn = 1
-- Loop throug all columns of the index and append them to the CREATE statement
OPEN cIxColumn
FETCH NEXT FROM cIxColumn INTO @IxColumn
WHILE (@@FETCH_STATUS = 0)
BEGIN
IF (@IxFirstColumn = 1)
SET @IxFirstColumn = 0
ELSE
SET @IXSQL = @IXSQL + ', '
SET @IXSQL = @IXSQL + @IxColumn
FETCH NEXT FROM cIxColumn INTO @IxColumn
END
CLOSE cIxColumn
DEALLOCATE cIxColumn
SET @IXSQL = @IXSQL + ')'
-- Print out the CREATE statement for the index
PRINT @IXSQL
FETCH NEXT FROM cIX INTO @IxTable, @IxTableID, @IxName, @IxID
END
CLOSE cIX
DEALLOCATE cIX
GO
Declare @TableName VarChar (Max), @IndexScript VarChar (Max)
Exec ScriptIndex 'Client', @IndexScript OUTPUT
Print @IndexScript
答案 2 :(得分:4)
编辑:这取决于原始和更改的数据类型。 如果您尝试将列从varchar更改为nvarchar,则会失败。 然而,如果您将列从varchar(16)更改为varchar(32),它将成功。
--Disable Index
ALTER INDEX MyIndex ON MyTable DISABLE
GO
-- Change column datatype
--Enable Index
ALTER INDEX MyIndex ON MyTable REBUILD
GO
如果更改列的类型,则必须重建使用该列的所有索引。
但除非您拥有大量数据(或全天候运行),否则重建索引并不是什么大问题。只需安排一个维护窗口。
答案 3 :(得分:0)
最好的办法是创建一个返回给定表/列的索引脚本的过程。因此,您可以仅从正在更改的列中删除索引,而不是从表中删除所有索引,而创建索引可能有些昂贵。
重建存储在数据表中的索引
-- objective : Generates indices scripting using specified column
-- Parameters :
-- @Tabela -> Name of the table that the column belongs to
-- @Coluna -> Name of the column that will be searched for the indices to generate the script
--Use: proc_ScriptIndexColumn 'TableName', 'CollumnName'
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
Create Proc proc_ScriptIndexColumn (@Tabela VARCHAR(4000), @Coluna VARCHAR(4000))
AS
BEGIN
DECLARE @isql_key VARCHAR(4000),
@isql_incl VARCHAR(4000),
@tableid INT,
@indexid INT
DECLARE @tablename VARCHAR(4000),
@indexname VARCHAR(4000)
DECLARE @isunique INT,
@isclustered INT,
@indexfillfactor INT
DECLARE @srsql VARCHAR(MAX)
DECLARE @ScriptsRetorno TABLE
(Script VARCHAR(MAX))
DECLARE index_cursor CURSOR
FOR
SELECT tablename = OBJECT_NAME(i.[object_id]),
tableid = i.[object_id],
indexid = i.index_id,
indexname = i.name,
isunique = i.is_unique,
CASE I.type_desc
WHEN 'CLUSTERED' THEN 1
ELSE 0
END AS isclustered,
indexfillfactor = i.fill_factor
FROM sys.indexes AS i
INNER JOIN SYSOBJECTS AS O
ON I.[object_id] = O.ID
INNER JOIN sys.index_columns AS ic
ON (ic.column_id > 0
AND (ic.key_ordinal > 0
OR ic.partition_ordinal = 0
OR ic.is_included_column != 0
))
AND ( ic.index_id = CAST(i.index_id AS INT)
AND ic.object_id = i.[object_id]
)
INNER JOIN sys.columns AS sc
ON sc.object_id = ic.object_id
AND sc.column_id = ic.column_id
WHERE O.XTYPE = 'U'
AND i.typE = 2 /*Non clustered*/
AND i.is_unique = 0
AND i.is_hypothetical = 0
AND UPPER(OBJECT_NAME(i.[object_id])) = UPPER(@Tabela)
AND UPPER(sc.name) = UPPER(@Coluna)
OPEN index_cursor
FETCH NEXT FROM index_cursor INTO @tablename,@tableid, @indexid,@indexname ,
@isunique ,@isclustered , @indexfillfactor
WHILE @@fetch_status <> -1
BEGIN
SELECT @isql_key = '',
@isql_incl = ''
SELECT @isql_key = CASE ic.is_included_column
WHEN 0 THEN CASE ic.is_descending_key
WHEN 1 THEN @isql_key +COALESCE(sc.name, '') +
' DESC, '
ELSE @isql_key + COALESCE(sc.name, '')
+ ' ASC, '
END
ELSE @isql_key
END,
--include column
@isql_incl = CASE ic.is_included_column
WHEN 1 THEN CASE ic.is_descending_key
WHEN 1 THEN @isql_incl +
COALESCE(sc.name, '') +
', '
ELSE @isql_incl + COALESCE(sc.name, '')
+ ', '
END
ELSE @isql_incl
END
FROM sysindexes i
INNER JOIN sys.index_columns AS ic
ON (
ic.column_id > 0
AND (
ic.key_ordinal > 0
OR ic.partition_ordinal = 0
OR ic.is_included_column != 0
)
)
AND (ic.index_id = CAST(i.indid AS INT) AND ic.object_id = i.id)
INNER JOIN sys.columns AS sc
ON sc.object_id = ic.object_id
AND sc.column_id = ic.column_id
WHERE i.indid > 0
AND i.indid < 255
AND (i.status & 64) = 0
AND i.id = @tableid
AND i.indid = @indexid
ORDER BY
i.name,
CASE ic.is_included_column
WHEN 1 THEN ic.index_column_id
ELSE ic.key_ordinal
END
IF LEN(@isql_key) > 1
SET @isql_key = LEFT(@isql_key, LEN(@isql_key) -1)
IF LEN(@isql_incl) > 1
SET @isql_incl = LEFT(@isql_incl, LEN(@isql_incl) -1)
SET @srsql = 'CREATE ' + 'INDEX [' + @indexname + ']' + ' ON [' + @tablename
+ '] '
SET @srsql = @srsql + '(' + @isql_key + ')'
IF (@isql_incl <> '')
SET @srsql = @srsql + ' INCLUDE(' + @isql_incl + ')'
IF (@indexfillfactor <> 0)
SET @srsql = @srsql + ' WITH ( FILLFACTOR = ' + CONVERT(VARCHAR(10), @indexfillfactor)
+ ')'
FETCH NEXT FROM index_cursor INTO @tablename,@tableid,@indexid,@indexname,
@isunique ,@isclustered , @indexfillfactor
INSERT INTO @ScriptsRetorno
VALUES
(@srsql)
END
CLOSE index_cursor
DEALLOCATE index_cursor
SELECT *
FROM @ScriptsRetorno
RETURN @@ERROR
END