[英]T-SQL: alter table to add a column that exists in another table
我正在使用SQL Server 2008中的两个表: foo
和foo_mod
,它们具有以下架构:
CREATE TABLE foo
(
[bar] DATETIME NULL ,
[bar1] VARCHAR(20) NULL ,
[different_column] VARCHAR(50) NOT NULL
)
CREATE TABLE foo_mod
(
[bar] DATETIME NULL ,
[bar1] VARCHAR(20) NULL
)
我想构建一个执行以下操作的SQL脚本:
对于foo
每一列,请检查foo_mod
中是否存在该列,如果不存在,请更改foo_mod
以添加缺少的列。
在此示例中,我的脚本将返回以下内容:
IF COL_LENGTH('foo_mod','bar') IS NULL BEGIN
ALTER TABLE foo_mod
ADD bar DATETIME NULLL;
END
IF COL_LENGTH('foo_mod','bar1') IS NULL BEGIN
ALTER TABLE foo_mod
ADD bar1 VARCHAR(20) NULL;
END
IF COL_LENGTH('foo_mod','different_column') IS NULL BEGIN
ALTER TABLE foo_mod
ADD different_column VARCHAR(50) NOT NULL;
END
现在,我的脚本使用游标从第一个表中遍历INFORMATION_SCHEMA.COLUMNS
:
DECLARE @column_name VARCHAR(max);
DECLARE @is_nullable VARCHAR(3);
DECLARE @data_type NVARCHAR(128);
DECLARE @default NVARCHAR(4000);
DECLARE @max_lengh INT;
DECLARE @sql VARCHAR(max);
DECLARE @output VARCHAR(max);
SET @output = '';
DECLARE col_names_cursor CURSOR
FOR
SELECT COLUMN_NAME, IS_NULLABLE, DATA_TYPE, COLUMN_DEFAULT, CHARACTER_MAXIMUM_LENGTH
FROM INFORMATION_SCHEMA.COLUMNS
WHERE TABLE_NAME = N'foo'
OPEN col_names_cursor
FETCH NEXT FROM col_names_cursor INTO @column_name, @is_nullable, @data_type,@default, @max_lengh;
WHILE @@FETCH_STATUS = 0
BEGIN
SET @sql = 'IF COL_LENGTH(''foo_mod'','''@column_name''') IS NULL BEGIN ALTER TABLE ''foo_mod'' ADD '
SET @sql += ? -- build sql script from informations
FETCH NEXT FROM col_names_cursor INTO @column_name, @is_nullable, @data_type,@default, @max_lengh;
END
CLOSE col_names_cursor;
DEALLOCATE col_names_cursor;
有没有一种简单的方法可以根据给定的信息构建SQL语句?
谢谢!
我倾向于在这里使用目录视图,而不是INFORMATION_SCHEMA
,因为INFORMATION_SCHEMA
不处理标识列或计算列:
为了说明这一点,我对表foo
些微改动:
CREATE TABLE foo
(
ID INT IDENTITY(1, 1),
[bar] DATETIME NULL ,
[bar1] VARCHAR(20) NULL ,
[different_column] VARCHAR(50) NOT NULL ,
ComputedColumn AS bar1 + different_column
)
然后,您可以查询目录视图以构建您的语句:
SELECT 'ALTER TABLE dbo.Foo_mod ADD ' + c.Name + ' ' +
CASE WHEN c.is_computed = 1 THEN 'AS ' + cc.definition
ELSE t.Name +
CASE WHEN c.is_identity = 1
THEN ' IDENTITY(' + CONVERT(VARCHAR(10), ic.seed_value) + ',' + CONVERT(VARCHAR(10), ic.increment_value) + ')'
WHEN t.name IN ('CHAR', 'NCHAR', 'VARCHAR', 'NVARCHAR', 'DATETIME2')
THEN '(' + CONVERT(VARCHAR(10), c.max_length) + ')'
WHEN t.name IN ('NUMERIC', 'DECIMAL')
THEN '(' + CONVERT(VARCHAR(10), c.precision) + ', ' + CONVERT(VARCHAR(10), c.scale) + ')'
ELSE ''
END
END + ';
GO
'
FROM sys.columns AS c
INNER JOIN sys.types AS t
ON t.system_type_id = c.system_type_id
AND t.user_type_id = c.user_type_id
LEFT JOIN sys.computed_columns AS cc
ON cc.object_id = c.object_id
AND cc.column_id = c.column_id
LEFT JOIN sys.identity_columns AS ic
ON ic.object_id = c.object_id
AND ic.column_id = c.column_id
WHERE c.object_id = OBJECT_ID(N'dbo.foo', 'U')
AND NOT EXISTS
( SELECT 1
FROM sys.columns AS c2
WHERE c2.object_id = OBJECT_ID(N'dbo.foo_mod')
AND c2.name = c.name
)
ORDER BY c.column_id;
会产生:
ALTER TABLE dbo.Foo_mod ADD ID int IDENTITY(1,1);
GO
ALTER TABLE dbo.Foo_mod ADD different_column varchar(50);
GO
ALTER TABLE dbo.Foo_mod ADD ComputedColumn AS ([bar1]+[different_column]);
GO
现在,您需要做的就是通过将行串联为一行将其捕获到变量中并执行它:
DECLARE @SQL NVARCHAR(MAX);
SELECT @SQL = (SELECT 'ALTER TABLE dbo.Foo_mod ADD ' + c.Name + ' ' +
CASE WHEN c.is_computed = 1 THEN 'AS ' + cc.definition
ELSE t.Name +
CASE WHEN c.is_identity = 1
THEN ' IDENTITY(' + CONVERT(VARCHAR(10), ic.seed_value) + ',' + CONVERT(VARCHAR(10), ic.increment_value) + ')'
WHEN t.name IN ('CHAR', 'NCHAR', 'VARCHAR', 'NVARCHAR', 'DATETIME2')
THEN '(' + CONVERT(VARCHAR(10), c.max_length) + ')'
WHEN t.name IN ('NUMERIC', 'DECIMAL')
THEN '(' + CONVERT(VARCHAR(10), c.precision) + ', ' + CONVERT(VARCHAR(10), c.scale) + ')'
ELSE ''
END
END + ';
GO
'
FROM sys.columns AS c
INNER JOIN sys.types AS t
ON t.system_type_id = c.system_type_id
AND t.user_type_id = c.user_type_id
LEFT JOIN sys.computed_columns AS cc
ON cc.object_id = c.object_id
AND cc.column_id = c.column_id
LEFT JOIN sys.identity_columns AS ic
ON ic.object_id = c.object_id
AND ic.column_id = c.column_id
WHERE c.object_id = OBJECT_ID(N'dbo.foo', 'U')
AND NOT EXISTS
( SELECT 1
FROM sys.columns AS c2
WHERE c2.object_id = OBJECT_ID(N'dbo.foo_mod')
AND c2.name = c.name
)
ORDER BY c.column_id
FOR XML PATH(''), TYPE).value('.', 'NVARCHAR(MAX)');
PRINT @SQL;
EXECUTE sp_executesql @SQL;
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.