[VIP专享]一个简单的去除重复字段的SQL查询语句

一个简单的去除重复字段的SQL查询语句

2009-11-16 17:12

一个简单的去除重复字段的SQL查询语句

[2008-11-04 16:01:15 by rainoxu] | 分类：我的知识库

今天公司里让.Net程序修改一个程序，需要去掉输出中的重复楼盘名称，一开始想到的是Distinct，但死路不通，只能改道，最终偶在网上找到了一个思路，修改了一下就有了。

先看所有记录（这是我在测试的数据库里做的）：

OK，我们这样来消除重复项：

1.

select * from table1 as a

where not exists(select 1 from table1 where logID=a.LogID and ID>a.ID)

2.

最近做一个数据库的数据导入功能，发现联合主键约束导致不能导入，原因是源表中有重复数据，但是源表中又没有主键，很是麻烦。经过努力终于解决了，现在就来和大家分享一下，有更好的办法的可以相互交流。

有重复数据主要有一下几种情况：

1.存在两条完全相同的纪录

这是最简单的一种情况，用关键字distinct就可以去掉

example：select distinct * from table(表名) where (条件)

2.存在部分字段相同的纪录（有主键id即唯一键）

如果是这种情况的话用distinct是过滤不了的，这就要用到主键id 的唯一性特点及group by分组

example:

select * from table where id in (select max(id) from table group by [去除重复的字段名列表,....])

3.没有唯一键ID

这种情况我觉得最复杂，目前我只会一种方法，有那位知道其他方法的可以留言，交流一下：

example:

select identity(int1,1) as id,* into newtable(临时表) from table select * from newtable where id in (select max(id) from newtable group by [去除重复的字段名列表,....])

drop table newtable

关于一个去除重复记录的sql语句

2009-8-24 16:33

提问者：lichuanbao1234|悬赏分：30 |浏览次数：1075次

我要查询一个表中content字段相同的记录的详细信息。其中每条记录都有一个标识符state，0表示未发送，1表示已发送。我要统计所有content相同的记录的信息，包括其中已发送（state=1）的记录。请问大家看看我这样写有什么问题？

select distinct content,name,push_date,total,e.total_sended from

tbl_jingwei_push a,

(select count(*) as total_sended from tbl_jingwei_push where state=1 and content=a.content) e

这样查出的其他字段都是符合要求的，唯独e.total_sended的结果出问题，它显示的是表中所有state=1的记录，请问大家我要怎么改呢？

问题补充：

这个sql语句是不对的。表a是错误的。请大家指点迷津，我要统计content 相同并且state为1的记录数目。谢谢各位。我就是想去掉重复记录并统计一下，只不过如果state=1的话，我要统计一下state=1的记录数。前提是这些记录的content是相同的。

二楼回答的不对，这和我写的是一样的，a表是不能在e表中用的。

2009-8-24 16:57

最佳答案

select distinct content,name,push_date,total,sum(case state when 1 then 1 when 0 then 0 end) as total_sended from tbl_jingwei_push

以上，希望对你有所帮助！

select distinct content,name,push_date,total,e.total_sended from

tbl_jingwei_push a,

(select count(*) as total_sended from tbl_jingwei_push where state=1 and e.content=a.content) e

|评论

2009-8-24 16:54 hrhero|五级

select distinct content,name,push_date,total,e.total_sended from

tbl_jingwei_push a,

(select count(*) as total_sended from tbl_jingwei_push where state=1 and content=a.content group by content ) e

试试这样

SQLServer：Distinct和Group by去除重复字段记录

2010-10-14 11:31:27| 分类：默认分类 | 标签：|字号大中小订阅

重复记录有两个意义，一是完全重复的记录，也即所有字段均重复的记录

二是部分关键字段重复的记录，比如Name字段重复，而其他字段不一定重复或

都重复可以忽略。

1、对于第一种重复，比较容易解决，使用

select distinct * from tableName

就可以得到无重复记录的结果集。

如果该表需要删除重复的记录(重复记录保留1条)，可以按以下方法删除

select distinct * into #Tmp from tableName

drop table tableName

select * into tableName from #Tmp

drop table #Tmp

发生这种重复的原因是表设计不周产生的，增加唯一索引列即可解决。

2、这类重复问题通常要求保留重复记录中的第一条记录，操作方法如下

假设有重复的字段为Name,Address，要求得到这两个字段唯一的结果集 select identity(int,1,1) as autoID, * into #Tmp from tableName select min(autoID) as autoID into #Tmp2 from #Tmp group by Name select * from #Tmp where autoID in(select autoID from #tmp2)

最后一个select即得到了Name，Address不重复的结果集(但多了一个autoID字段，

实际写时可以写在select子句中省去此列)

其它的数据库可以使用序列，如：

create sequence seq1;

select seq1.nextval as autoID, * into #Tmp from tableName

============

zuolo: 我根据上面实例得到所需要的语句为SELECT MAX(id) AS ID,Prodou_id,FinalDye FROM anwell..tblDBDdata GROUP BY Prodou_id,FinalDye ORDER BY id，之前一直想用Distinct来得到指定字段不重复的记录是个误区。

如何写一个SQL语句，能检索出所有某个字段内容有重复的记录

A :

比如：

Name Adress Tele

1 Yao China 110

2 Zhang Moon 110

3 Wang China 110

4 Wang China 110

5 Yao China 110

根据姓名字段检索以后，能筛选出的记录有：1，3，4，5

select b.id from table as b,(select count(field),field from table where count(field)>2 group by field) as a where a.field=b.field

SELECT id from tb where dcount("id","tb","name='"&name&"'")>1

附:

DCount Function

See Also Specifics

You can use the DCount function to determine the number of records that are in a specified set of records (a domain). Use the DCount function in Visual Basic, a macro, a query expression, or a calculated control.

For example, you could use the DCount function in a module to return the number of records in an Orders table that correspond to orders placed on a particular date.

DCount(expr, domain, [criteria])

The DCount function has the following arguments.

Argument Description

expr An expression that identifies the field for which you want to count records. It can be a string expression identifying a field in a table or query, or it can be an expression that performs a calculation on data in that field. In expr, you can include the name of a field in a table, a control on a form, a constant, or a function. If expr includes a function, it can be either built-in or user-defined, but not another domain aggregate or SQL aggregate function.

domain A string expression identifying the set of records that constitutes the domain. It can be a table name or a query name for a query that does not require a parameter.

criteria An optional string expression used to restrict the range of data on which the DCount function is performed. For example, criteria is often equivalent to the WHERE clause in an SQL expression, without the word WHERE. If criteria is omitted, the DCount function evaluates expr against the entire domain. Any field that is included in criteria must also be a field in domain; otherwise the DCount function returns a Null.

Remarks

Use the DCount function to count the number of records in a domain when you don't need to know their particular values. Although the expr argument can perform a calculation on a field, the DCount function simply tallies the number of records. The value of any calculation performed by expr is unavailable.

Use the DCount function in a calculated control when you need to specify criteria to restrict the range of data on which the function is performed. For example, to display the number of orders to be shipped to California, set the ControlSource property of a text box to the following expression:

=DCount("[OrderID]", "Orders", "[ShipRegion] = 'CA'")

If you simply want to count all records in domain without specifying any restrictions, use the Count function.

Tip The Count function has been optimized to speed counting of records in queries. Use the Count function in a query expression instead of the DCount function, and set optional criteria to enforce any restrictions on the results. Use the DCount function when you must count records in a domain from within a code module or macro, or in a calculated control.

You can use the DCount function to count the number of records containing a particular field that isn't in the record source on which your form or report is based. For example, you could display the number of orders in the Orders table in a calculated control on a form based on the Products table.

The DCount function doesn't count records that contain Null values in the field referenced by expr unless expr is the asterisk (*) wildcard character. If you use an asterisk, the DCount function calculates the total number of records, including those that contain Null fields. The following example calculates the number of records in an Orders table.

intX = DCount("*", "Orders")

If domain is a table with a primary key, you can also count the total number of records by setting expr to the primary key field, since there will never be a Null in the primary key field.

If expr identifies multiple fields, separate the field names with a concatenation operator, either an ampersand (&) or the addition operator (+). If you use an ampersand to separate the fields, the DCount function returns the number of records containing data in any of the listed fields. If you use the addition operator, the DCount function returns only the number of records containing data in all of the listed fields. The following example demonstrates the effects of each operator when used with a field that contains data in all records (ShipName) and a field that contains no data (ShipRegion).

intW = DCount("[ShipName]", "Orders")

intX = DCount("[ShipRegion]", "Orders")

intY = DCount("[ShipName] + [ShipRegion]", "Orders")

intZ = DCount("[ShipName] & [ShipRegion]", "Orders")

Note The ampersand is the preferred operator for performing string concatenation. You should avoid using the addition operator for anything other than numeric addition, unless you specifically wish to propagate Nulls through an expression.

Unsaved changes to records in domain aren't included when you use this function. If you want the DCount function to be based on the changed values, you must first save the changes by clicking Save Record on the Records menu, moving the focus to another record, or by using the Update method.

Example

The following function returns the number of orders shipped to a specified country after a specified ship date. The domain is an Orders table.

Public Function OrdersCount(ByVal strCountry As String, _

ByVal dteShipDate As Date) As Integer

OrdersCount = DCount("[ShippedDate]", "Orders", _

"[ShipCountry] = '" & strCountry & _

"' AND [ShippedDate] > #" & dteShipDate & "#")

End Function

To call the function, use the following line of code in the Immediate window:

:OrdersCount "UK", #1/1/96#

我现在正在DAO里面，头都大了

就用简单的吧

CString strSQL;

帮我把上面那一句怎么放入CString 里面？