A Set is a Collection that cannot contain duplicate elements. It models the mathematical set abstraction. The Set interface contains only methods inherited from Collection and adds the restriction that duplicate elements are prohibited. Two Set instances are equal if they contain the same elements.

Duplicate describes something that’s an exact copy. The verb duplicate is pronounced differently, with a long a sound, and it means to make a copy of or to multiply times two. The Latin root, duplicatus, means “to double.”

1a : either of two things exactly alike and usually produced at the same time or by the same process. b : an additional copy of something (such as a book or stamp) already in a collection. 2 : one that resembles or corresponds to another : counterpart. 3 : two identical copies —used in the phrase in duplicate.

in duplicate, in two copies, especially two identical copies: Please type the letter in duplicate.

Duplicate in a Sentence ?

1. The man’s duplicate license replaced the original that he lost.
2. A duplicate copy of the infant’s birth certificate was requested by his parents.
3. A duplicate photo was needed after the first framed picture broke.

2) Duplicates: HashSet does’t allow duplicate values. HashMap store key, value pairs and it does not allow duplicate keys. If key is duplicate then old key is replaced with new value.

ArrayList allows duplicate values while HashSet doesn’t allow duplicates values. Ordering : ArrayList maintains the order of the object in which they are inserted while HashSet is an unordered collection and doesn’t maintain any order.

To make sure that rows in a table are unique, some column or combination of columns must be required to contain unique values in each row. The following table contains no such index, so it would allow duplicate rows: CREATE TABLE person ( last_name CHAR(20), first_name CHAR(20), address CHAR(40) );

The meaning of “sets do not allow duplicate values” is that when you add a duplicate to a set, the duplicate is ignored, and the set remains unchanged. This does not lead to compile or runtime errors: duplicates are silently ignored. Internally SET store element using HASHTABLE …

Multi-valued lookup or attachment fields cannot contain duplicate values.

Preventing Duplicates from Occurring in a Table. You can use a PRIMARY KEY or a UNIQUE Index on a table with the appropriate fields to stop duplicate records. Let us take an example – The following table contains no such index or primary key, so it would allow duplicate records for first_name and last_name.

To delete the duplicate rows from the table in SQL Server, you follow these steps:

1. Find duplicate rows using GROUP BY clause or ROW_NUMBER() function.
2. Use DELETE statement to remove the duplicate rows.

1. Backup your original table.
2. Make sure your backup is good and you can restore original table if you need to.
3. Create a temporary table with unique records using DISTINCT clause.
4. Delete all records from original table.
5. Insert all records from temporary table into original table.
6. Verify your results and commit your work.

The go to solution for removing duplicate rows from your result sets is to include the distinct keyword in your select statement. It tells the query engine to remove duplicates to produce a result set in which every row is unique. The group by clause can also be used to remove duplicates.

You are getting duplicates because more than one row matches your conditions. To prevent duplicates use the DISTINCT keyword: SELECT DISTINCT respid, cq4_1, dma etc… If you do not have duplicates in preweighting_data before then the only other chance is, that the column us_zip.

How to Find Duplicate Values in SQL

1. Using the GROUP BY clause to group all rows by the target column(s) – i.e. the column(s) you want to check for duplicate values on.
2. Using the COUNT function in the HAVING clause to check if any of the groups have more than 1 entry; those would be the duplicate values.

Below are alternate solutions :

1. Remove Duplicates Using Row_Number. WITH CTE (Col1, Col2, Col3, DuplicateCount) AS ( SELECT Col1, Col2, Col3, ROW_NUMBER() OVER(PARTITION BY Col1, Col2, Col3 ORDER BY Col1) AS DuplicateCount FROM MyTable ) SELECT * from CTE Where DuplicateCount = 1.
2. Remove Duplicates using group By.

Select column values in a specific order within rows to make rows with duplicate sets of values identical. Then you can use SELECT DISTINCT to remove duplicates.

Remove duplicate values

1. Select the range of cells that has duplicate values you want to remove. Tip: Remove any outlines or subtotals from your data before trying to remove duplicates.
2. Click Data > Remove Duplicates, and then Under Columns, check or uncheck the columns where you want to remove the duplicates.
3. Click OK.

(1) Select Fruit column (which you will remove duplicates rows by), and then click the Primary Key button; (2) Select the Amount column (Which you will keep highest values in), and then click Calculate > Max. (3) Specify combination rules for other columns as you need.

Google Sheets: Remove duplicates from a spreadsheet

1. Select a column from where you want to remove the duplicates.
2. Click Data > Remove duplicates.
3. You will now see a pop-up. Tick the box next to Data has header now > click Remove duplicates > click Done.
4. You can repeat the steps for other columns as well.

Select the range you want to remove duplicate rows. If you want to delete all duplicate rows in the worksheet, just hold down Ctrl + A key to select the entire sheet. 2. On Data tab, click Remove Duplicates in the Data Tools group.

Excel always keeps the first data set of a duplicated row. All consecutive rows are removed.

Remove Duplicates from Multiple Columns in Excel

1. Select the data.
2. Go to Data –> Data Tools –> Remove Duplicates.
3. In the Remove Duplicates dialog box: If your data has headers, make sure the ‘My data has headers’ option is checked. Select all the columns except the Date column.

With a formula and the Filter function, you can quickly remove duplicates but keep rest.

1. Select a blank cell next to the data range, D2 for instance, type formula =A3=A2, drag auto fill handle down to the cells you need.
2. Select all data range including the formula cell, and click Data > Filter to enable Filter function.

To remove duplicates keep blank rows, you need to add a helper column to identify the blank rows firstly, then apply Remove Duplicates function to remove the duplicates.

Tip: You also can remove all duplicates but keep one with Select Duplicate & Unique Cells like this: Select all the unique values including the first duplicates, and then copy them by pressing Ctrl + C and paste to another location by Ctrl + V.

Go to the Design tab ➜ select Subtotals ➜ select Do Not Show Subtotals. You now have a pivot table that mimics a tabular set of data! Pivot tables only list unique values for items in the Rows area, so this pivot table will automatically remove any duplicates in your data.