SQL removes duplicate records, SQL removes duplicates

SQL removes duplicate records, SQL removes duplicates

There are two Repeated Records. One is a completely repeated record, that is, records with all fields being repeated, and the other is records with duplicate key fields, such as duplicate Name fields, other fields are not necessarily repeated or can be ignored.
1. For the first type of repetition, it is easier to solve.
Select distinct * from tableName
You can get the result set without repeated records.
If the table needs to delete duplicate records (one record is retained), you can delete the record as follows:
Select distinct * into # Tmp from tableName
Drop table tableName
Select * into tableName from # Tmp
Drop table # Tmp
The reason for this repetition is that the table design is not weekly. You can add a unique index column.

2. Repeat problems usually require that the first record in the repeat record be retained. The procedure is as follows:
Assume that the duplicate fields are Name and Address. You must obtain the unique result set of the two fields.
Select identity (int, 1, 1) as autoID, * into # Tmp from tableName
Select min (autoID) as autoID into # Tmp2 from # Tmp group by Name, Address
Select * from # Tmp where autoID in (select autoID from # tmp2)
The last select command gets the result set with no duplicate Name and Address (but an autoID field is added, which can be omitted in the select clause when writing)
Or
With Dups
(
Explain partition select *, row_number () over (partition by Product_Code order by Product_Code) as RowNum
Too many rows from # prod
)


Delete from Dups where rownum> 1;

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The record for self-use distinct is as follows:

<! -- Customer Batch List --> <select id = "listPageCusBatch" parameterType = "paramMap" resultType = "pd"> select distinct tp. post_batchNo, tp. post_time, tp. customer_id, tc. customer_name FROM tb_dispatch_mail_post tp left join tb_dispatch_customer tc ON tp. customer_id = tc. customer_id <where> tp. post_batchno is not null <if test = "paramMap. postTimeStart! = Null and paramMap. postTimeStart. length ()> 0 "> AND TO_DATE (# {paramMap. postTimeStart}, 'yyyy-mm-dd hh24: mi: ss') <= tp. post_time </if> <if test = "paramMap. postTimeEnd! = Null and paramMap. postTimeEnd. length ()> 0 "> AND TO_DATE (# {paramMap. postTimeEnd}, 'yyyy-mm-dd hh24: mi: ss')> = tp. post_time </if> </where> order by tp. post_batchno DESC </select>