SQL statement used to query and delete duplicate data in a data table

SQL statement used to query and delete duplicate data in a data table

1. query duplicate data in the table. Select * from people Where peopleId in (select peopleId from people group by peopleId having count (peopleId)> 1) 2. Delete unnecessary duplicate records in the Table. Repeat records are determined based on a single field (eagleid), leaving only the records with the smallest rowid Delete from people Where peopleId in (select peopleId from people group by peopleId having count (peopleId)> 1) And rowid not in (select min (rowid) from people group by peopleId having count (peopleId)> 1) 3. Search for redundant duplicate records in the table (multiple fields) Elect * from vitae Where (a. peopleId, a. seq) in (select peopleId, seq from vitae group by peopleId, seq having count (*)> 1) 4. Delete redundant record (multiple fields) in the table, leaving only the records with the smallest rowid Delete from vitae Where (a. peopleId, a. seq) in (select peopleId, seq from vitae group by peopleId, seq having count (*)> 1) And rowid not in (select min (rowid) from vitae group by peopleId, seq having count (*)> 1) 5. Search for redundant duplicate records (multiple fields) in the table, excluding records with the smallest rowid Select * from vitae Where (a. peopleId, a. seq) in (select peopleId, seq from vitae group by peopleId, seq having count (*)> 1) And rowid not in (select min (rowid) from vitae group by peopleId, seq having count (*)> 1) (2) For example There is A field "name" in Table ", The "name" value may be the same for different records, Now, you need to query items with duplicate "name" values between records in the table; Select Name, Count (*) From A Group By Name Having Count (*)> 1 If the gender is also the same, the statement is as follows: Select Name, sex, Count (*) From A Group By Name, sex Having Count (*)> 1 (3) Method 1 Declare @ max integer, @ id integer Declare cur_rows cursor local for select Main field, count (*) from table name group by main field having count (*)>; 1 Open cur_rows Fetch cur_rows into @ id, @ max While @ fetch_status = 0 Begin Select @ max = @ max-1 Set rowcount @ max Delete from table name where primary field = @ id Fetch cur_rows into @ id, @ max End Close cur_rows Set rowcount 0 Method 2 "Repeat record" has two duplicate records. One is a completely repeated record, that is, a record with all fields already exists. The other is a record with duplicate key fields, for example, the Name field is repeated, while 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, autoID 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) (4) Duplicate Query Select * from tablename where id in (select id from tablename group by id Having count (id)> 1)