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Oracle - remove - remove duplicates sql. Deleting records from SQL Sql database fast deleting records from oracle table

delete by rowid oracle (14)

I'm testing something in Oracle and populating a table with some example data, but in the process I accidentally loaded duplicate records, so now I can't create a primary key using some of the columns.

How to remove all duplicate lines and leave only one of them?

Solution 1)

delete from emp where rowid not in (select max(rowid) from emp group by empno);

Solution 2)

delete from emp where rowid in (select rid from (select rowid rid, row_number() over(partition by empno order by empno) rn from emp) where rn > 1);

Solution 3)

For better performance, here's what I wrote:
(see execution plan)

DELETE FROM your_table WHERE rowid IN (select t1.rowid from your_table t1 LEFT OUTER JOIN (SELECT MIN(rowid) as rowid, column1,column2, column3 FROM your_table GROUP BY column1, column2, column3) co1 ON (t1.rowid = co1. rowid) WHERE co1.rowid IS NULL);

Check below scripts -

Create table test(id int,sal int);

insert into test values(1,100); insert into test values(1,100); insert into test values(2,200); insert into test values(2,200); insert into test values(3,300); insert into test values(3,300); commit;

select * from test;

You will see 6 entries here.
4.run below query -

Delete from test where rowid in (select rowid from (select rowid, row_number() over (partition by id order by sal) dup from test) where dup > 1)

select * from test;

You will see that the duplicate entries have been removed.
Hope this solves your request. Thanks to:)

To select duplicates, only the query format can be:

SELECT GroupFunction(column1), GroupFunction(column2),..., COUNT(column1), column1, column2... FROM our_table GROUP BY column1, column2, column3... HAVING COUNT(column1) > 1

So the correct query on the other suggestion is:

DELETE FROM tablename a WHERE a.ROWID > ANY (SELECT b.ROWID FROM tablename b WHERE a.fieldname = b.fieldname AND a.fieldname2 = b.fieldname2 AND ....so on.. to identify the duplicate rows.. ..)

This query will save the most old record in the database for the criteria selected in the WHERE CLAUSE .

Oracle Certified Associate (2008)

I haven't seen answers that use common table expressions and window functions. It's the one that's easiest for me to work with.

DELETE FROM YourTable WHERE ROWID IN (WITH Duplicates AS (SELECT ROWID RID, ROW_NUMBER() OVER(PARTITION BY First_Name, Last_Name, Birth_Date) AS RN SUM(1) OVER(PARTITION BY First_Name, Last_Name, Birth_Date) ORDER BY ROWID ROWS BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) AS CNT FROM YourTable WHERE Load_Date IS NULL) SELECT RID FROM duplicates WHERE RN > 1);

Things to note:

1) We only check for duplicate fields in a section.

2) If you have a reason to choose one duplicate over the others, you can use the order by clause so that this row has row_number() = 1

3) You can change the duplicate number stored by changing the final where clause to "Where RN>N" with N>=1 (I thought N=0 would remove all rows with duplicates, but just remove all rows).

4) Added a Sum section field, a CTE query that will label each fow with the row numbers in the group. So to select rows with duplicates, including the first element, use "WHERE cnt > 1".

1. decision

Delete from emp where rowid not in (select max(rowid) from emp group by empno);

2. solution

Delete from emp where rowid in (select rid from (select rowid rid, row_number() over(partition by empno order by empno) rn from emp) where rn > 1);

3.solution

Delete from emp e1 where rowid not in (select max(rowid) from emp e2 where e1.empno = e2.empno);

4. solution

Delete from emp where rowid in (select rid from (select rowid rid, dense_rank() over(partition by empno order by rowid) rn from emp) where rn > 1);

Create or replace procedure delete_duplicate_enq as cursor c1 is select * from enquiry; begin for z in c1 loop delete enquiry where enquiry.enquiryno = z.enquiryno and rowid > any (select rowid from enquiry where enquiry.enquiryno = z.enquiryno); end-loop; end delete_duplicate_enq;

Create table abcd(id number(10),name varchar2(20)) insert into abcd values(1,"abc") insert into abcd values(2,"pqr") insert into abcd values(3,"xyz") insert into abcd values(1,"abc") insert into abcd values(2,"pqr") insert into abcd values(3,"xyz") select * from abcd id Name 1 abc 2 pqr 3 xyz 1 abc 2 pqr 3 xyz Delete Duplicate record but keep Distinct Record in table DELETE FROM abcd a WHERE ROWID > (SELECT MIN(ROWID) FROM abcd b WHERE b.id=a.id); run the above query 3 rows delete select * from abcd id Name 1 abc 2 pqr 3 xyz

Deleting entries

The DELETE statement is used to remove records from a table:

DELETE FROM tablename WHERE condition;

This statement removes from the specified table records (not individual column values) that satisfy the specified condition. Condition is a boolean expression, various designs which have been covered in previous labs.

The following query removes records from the Customer table in which the value of the LName column is "Ivanov":

DELETE FROM Customer

WHERE LName = "Ivanov"

If the table contains information about several clients with the last name Ivanov, then all of them will be deleted.

The WHERE clause can contain a subquery to select data (the SELECT statement). Subqueries in a DELETE statement work exactly the same way as they do in a SELECT statement. The following query removes all customers from the city of Moscow, with the city's unique identifier returned using a subquery.

DELETE FROM Customer

WHERE IdCity IN (SELECT IdCity FROM City WHERE CityName = "Moscow")

Transact-SQL extends standard SQL by allowing you to use another FROM clause in a DELETE statement. This join extension can be used instead of a subquery in the WHERE clause to specify the rows to be deleted. It allows you to set data from the second FROM and remove the corresponding rows from the table in the first FROM clause. In particular, the previous query could be rewritten as follows

DELETE FROM Customer

FROM Customer k INNER JOIN

The operation of deleting records from a table is dangerous in the sense that it is associated with the risk of irreversible data loss in case of semantic (but not syntactic) errors in the formulation of the SQL statement. To avoid trouble, before deleting records, we recommend that you first run the appropriate select query to see which records will be deleted. So, for example, before executing the delete query discussed earlier, it would not hurt to execute the corresponding select query.

SELECT *

FROM Customer k INNER JOIN

City c ON k.IdCity = c.IdCity AND c.CityName = "Moscow"

To remove all records from a table, just use the DELETE statement without keyword WHERE. At the same time, the table itself with all the columns defined in it is saved and ready for inserting new records. For example, the following query removes records for all products.

DELETE FROM Product

Task for independent work: Formulate on SQL language a request to delete all orders that do not contain any goods (i.e. all empty orders).

Removing duplicate rows from a table in Oracle (14)

Solution 1)

delete from emp where rowid not in (select max(rowid) from emp group by empno);

Solution 2)

delete from emp where rowid in (select rid from (select rowid rid, row_number() over(partition by empno order by empno) rn from emp) where rn > 1);

Solution 3)

How to remove all duplicate lines and leave only one of them?

For better performance, here's what I wrote:
(see execution plan)

Check below scripts -

Create table test(id int,sal int);

insert into test values(1,100); insert into test values(1,100); insert into test values(2,200); insert into test values(2,200); insert into test values(3,300); insert into test values(3,300); commit;

select * from test;

You will see 6 entries here.
4.run below query -

Delete from test where rowid in (select rowid from (select rowid, row_number() over (partition by id order by sal) dup from test) where dup > 1)

select * from test;

You will see that the duplicate entries have been removed.
Hope this solves your request. Thanks to:)

To select duplicates, only the query format can be:

SELECT GroupFunction(column1), GroupFunction(column2),..., COUNT(column1), column1, column2... FROM our_table GROUP BY column1, column2, column3... HAVING COUNT(column1) > 1

So the correct query on the other suggestion is:

DELETE FROM tablename a WHERE a.ROWID > ANY (SELECT b.ROWID FROM tablename b WHERE a.fieldname = b.fieldname AND a.fieldname2 = b.fieldname2 AND ....so on.. to identify the duplicate rows.. ..)

This query will store the oldest entry in the database for the criteria selected in the WHERE CLAUSE .

Oracle Certified Associate (2008)

I haven't seen answers that use common table expressions and window functions. It's the one that's easiest for me to work with.

Things to note:

1) We only check for duplicate fields in a section.

2) If you have a reason to choose one duplicate over the others, you can use the order by clause so that this row has row_number() = 1

3) You can change the duplicate number stored by changing the final where clause to "Where RN>N" with N>=1 (I thought N=0 would remove all rows with duplicates, but just remove all rows).

4) Added a Sum section field, a CTE query that will label each fow with the row numbers in the group. So to select rows with duplicates, including the first element, use "WHERE cnt > 1".

1. decision

Delete from emp where rowid not in (select max(rowid) from emp group by empno);

2. solution

Delete from emp where rowid in (select rid from (select rowid rid, row_number() over(partition by empno order by empno) rn from emp) where rn > 1);

3.solution

Delete from emp e1 where rowid not in (select max(rowid) from emp e2 where e1.empno = e2.empno);

4. solution

Delete from emp where rowid in (select rid from (select rowid rid, dense_rank() over(partition by empno order by rowid) rn from emp) where rn > 1);

The Oracle platform allows you to delete rows from tables, views, materialized views, nested subqueries, and partitioned views and tables as follows.

(table_name | ONLY (table_name)) [alias] [(PARTITION (partition_name) SUBPARTITION

(subsection_name))] | (subquery )]) | TABLE (collection_expression) [(+)])

INTO variable [, …]]

The parameters are shown below.

table_name [alias]

Specifies the table, view, materialized view, or partitioned table or view from which to delete records. Optionally, you can precede the table_name with a schema, or specify a database connection after the table name. Otherwise Oracle will use the current schema and local server Database. Optionally, you can give the table_name an alias. The alias is required if the table refers to an attribute or method of an object type.

PARTITION partition name

The delete operation is applied to the specified partition, not to the entire table. When deleting from a partitioned table, it is not necessary to specify the partition name, but in many cases it helps to reduce the complexity of the WHERE clause.

SUBPARTITION (subpartition_name)

The deletion is applied to the specified subkey, not to the entire table.

(subquery )])

Specifies that the target of the delete operation is a nested subquery and not a table, view, or other database object. The parameters of this proposal are as follows.

subquery

A SELECT statement is specified, which is a subquery. You can create any standard subquery, but it cannot contain ORDER BY clauses.

WITH READ ONLY

Indicates that the subquery cannot be updated.

WITH CHECK OPTION

Oracle will reject any changes to the remote table that are not visible in the result set of the subquery.

CONSTRAINT constraint_name

The Oracle system will restrict the changes you make based on the constraint named constraint_name.

TABLE (expression For rollection) [(+)]

The Oracle system will treat rollexpression as a table, although it could actually be a subquery, function, or other collection constructor. In either case, the value returned by the For Rollection expression must be a nested table or VARRAY.

RETURNING expression

Retrieves the rows affected by the command where the DELETE command would normally only return a count deleted rows. The RETURNING clause can be used if the target of the command is a table, a materialized view, or a view on a single base table. If the clause is used when deleting a single row, then the values from the deleted row that are determined by the expression are stored in PL/SQL variables and bind variables. If the clause is used when deleting multiple rows, then the values from the deleted rows that are determined by the expression are stored in the bind arrays.

INTO variable

Variables are specified into which the values returned as a result of the RETURNING clause are written.

When executing a DELETE statement, Oracle returns the space freed up in the table (or underlying view table) back to the table or index where the data was stored.

If data is removed from a view, the view cannot contain set operations, the DISTINCT keyword, joins, an aggregate function, an analytic function, SELECT subqueries, a GROUP BY clause, an ORDER BY clause, a CONNECT BY clause, or a START WITH clause.

Below is an example where we delete data from a remote server.

DELETE FROM scott [email protected];

In the following example

we are deleting data from the derived table specified in the expression for the collection.

DELETE TABLE(SELECT contactname FROM customers

with WHERE c.customerid="BOTTM") s WHERE s. region IS NULL OR s.country="MEXICO";

And here is an example of deletion from the section.

DELETE FROM sales PARTITION (sales_q3_1997) WHERE qty > 10000;

Finally, in the following example, we use the RETURNING clause to see the deleted values.

DELETE FROM employee WHERE job_id=13

AND hire_date + TO_YMINTERVAL("01-06") =.

The previous example removes records from the employee table and returns j obi vl values to a predefined variable: intol.

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Oracle - remove - remove duplicates sql. Deleting records from SQL Sql database fast deleting records from oracle table

delete by rowid oracle (14)

Solution 1)

Solution 2)

Solution 3)

Removing duplicate rows from a table in Oracle (14)

Solution 1)

Solution 2)

Solution 3)