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Do you know how to delete the duplicate records in SQL or how to delete duplicate rows in SQL? This blog will make you understand about all the queries like sql delete duplicate rows and records.
A Delete Query in SQL is used to delete a set of records, duplicate rows, table etc. based on the criterion specified. This is one of the most fundamental features of RDBMS because you had the flexibility to delete multiple records together even when they are linked to different tables to make the data management easier and more flexible.
A depth understanding of SQL delete query in SQL will improve the performance of database apps and makes you a highly skilled resource for the IT Companies. Obviously, you can delete duplicate entries manually as well but the process is time-consuming and difficult to maintain.
Read: Online SQL Queries for Practice Questions with Answers
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The objective of Delete command in SQL is to delete rows that are no longer needed in the database tables. It will delete the entire row from the table and is very handy to manage the temporary or obsolete data in the database. This is possible to delete multiple rows in the database with a single query only. It is proven more advantageous when you need to delete multiple entries or duplicate rows from the table. Once you will delete rows from the table, it cannot be recovered back. So, you are strongly recommended to take the data backup before you start making changes to the database tables. It will allow you to restore important data in the case of wrong use of the command that was actually important for the database application. Before we move further, we recommend you to take a demo session of SQL to see if you want to keep learning and get your basics stronger.
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The basic syntax of the delete command in SQL is given as below – DELETE FROM ‘table_name’ [WHERE condition]; The syntax with the “DELETE FROM” would explain to the server that something has to be deleted from the table. After the keyword, you need to add the table name and where condition in the end, if required. Where clause is optional in case of the SQL server and it is needed only when you want to restrict the delete operations based on the query. In case, you are not using the where clause then the entire table would be deleted. This is not possible to delete a particular column but you can delete the entire row from the table only.
Till the time, we have discussed the basic syntax used by beginners. Here, is an advanced form of Delete query in SQL or the full syntax that may be needed for large database apps – DELETE [TOP (top_value)] (PERCENT)] FROM table [WHERE conditions];
Top (top-value) – This is an optional field in SQL that would delete the top values from the database based on the values. For example, if you write TOP (10) then it will work on the first 10 values in the table only.
Read: Learn How to Add Column Using SQL Server ALTER TABLE ADD Column Statement
Percent – This is again an option field in the SQL where rows are deleted based on the percentage. For example, you can ask to delete only 5 percent of total rows within a database.
If you got a situation where you have to select the unique entries only from a particular database table then you have to be extra careful while fetching the records. So, how to write a syntax to fetch the unique values only not the duplicate entries? To overcome the situation, you should use the DISTINCT keyword along with the Select command in the SQL. Here, is how should you write the syntax to get your job done accurately-
SELECT DISTINCT column1, column2, ……..columnN FROM table_name WHERE [conditions]
This syntax will automatically delete the duplicate records in SQL and return unique values as needed.
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To delete an entire table in the SQL, you should use the following command as given below –
DELETE FROM table_name;
You just have to give the table name that you want to delete. In case, you are interested in deleting a particular row only then use the following command –
Read: How To Use The Exists Operator In The SQL?
DELETE FROM table_name [WHERE condition];
With the Where clause, you can quickly specify the conditions to restrict the delete operations. There are more similar operations like DELETE that include DROP and TRUNCATE but they are not necessarily the same and different from each other in possible ways.
Read: What Is The Difference Between Having And Where Clause In SQL?
For example, the Delete command in SQL only removes the database entries but it will not free up the space taken by the server. So, if you wanted to delete the table schema or properties as well then you should use the Truncate command in this case. So, the truncate command in SQL is not only used to delete the rows but it will free the containing space too. Here is the syntax for the Truncate command in the SQL –
TRUNCATE TABLE employee;
Next is the DROP command in SQL that will drop the table definition along with delete operation and all the relationships that are existing with the table are no longer valid. So, what are the features of DROP query in SQL ?
In the case of Truncate command in SQL, it will not delete the table structure, so you will not face the problems as given above. Based on the above discussion, you can quickly decide which command suits your database operations the most.
Deleting a single entry from the table is easy with the right command and the process. To delete a particular record from the table, the entry should look like this –
Read: SQL Having Clause Functions
DELETE FROM student_name WHERE id = 003;
Based on the syntax given above, it will delete the entire row with the ID 003 and output will be displayed as needed. Sometimes, the Delete query fails to run in the database if special permissions are set by the administrators. Here, you need to check first if you are permitted to make the changes in the table or not. Or you should log in as the administrator to make the required changes. If the database is set to the READ-ONLY mode then it cannot be modified. If the database is linked then it is not allowed to modify.
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If the table does not have a primary key then you are restricted to make the changes in the database table. Further, this is necessary to learn for you what is trivial data or historical data in SQL and how should you handle it?
This is a different scenario deleting trivial data from some temporary table and deleting historic data is a different aspect. You should know the difference between while working on two scenarios. Most of the time people consider deleting historic data that will never be used again. In case, you needed it later then it could be expensive and impossible sometimes.
Here, in this situation, two solutions are possible.
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Make sure that you spend enough time in learning and understanding the Delete command in the SQL and its different operations like how to delete a table, how to delete duplicate rows in SQL, how to delete records in SQL etc. With this article, you can save a lot of manual effort and there is no need to write unnecessary codes too. Keep in mind that with delete command, you are just hiding the record not deleting them completely. For permanent delete, this is always better using DROP or TRUNCATE commands.
Okay, now that you understand how you can delete duplicate records in sql and how to delete duplicate row in sql, we want to throw some light on Janbask Training where you can learn more such queries. You can also sign up for courses you find to be relevant.
Read: MySQL vs SQL Server vs Oracle: A Detailed Comparison
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