![]() ![]() Let us create a CUSTOMERS table using the following query −Īs we have not defined any constraints on the table, duplicate records can be inserted into it. These database constraints ensure that each entry in the specified column or set of columns is unique. To prevent the entry of duplicate records into a table, we can define a PRIMARY KEY or a UNIQUE Index on the relevant fields. This chapter will describe how to prevent the occurrence of duplicate records in a table and how to remove the already existing duplicate records. With increase in logical errors due to the presence of duplicates, the conclusions derived from data analysis in a database will also be erroneous. The existence of duplicates in an organizational database will lead to logical errors.ĭuplicate data occupies space in the storage, which leads to decrease in usage efficiency of a database.ĭue to the increased use of resources, the overall cost of the handling resources rises. Handling duplicates in an SQL database becomes necessary to prevent the following consequences − Why is Handling Duplicates in SQL Necessary? While in most cases, duplicates are allowed, there are situations where it is necessary to prevent duplicate records and remove them from a database table. If you liked this article, you must check out our Post Graduate Program in Full Stack Web Development as it covers the A-Z of SQL as well.ĭo you have any questions for us? Mention them in the comment section of our “Delete in SQL” article, and we’ll have our experts in the field answer them for you.Sometimes, tables or result sets contain duplicate records. Now that you know how to delete existing records, it is time for you to start learning about other SQL commands so that you can start manipulating and querying data and move forward in your journey to become an expert in SQL. ![]() Sometimes, we insert the wrong data, or the data in a table becomes outdated and needs modification, all of this requires the help of Delete in SQL.Ĭheck out our tutorials to learn how to delete duplicate rows in tables and many SQL statements. Next Stepsĭeleting records from tables and databases is a huge part of managing data. To check whether all the records have been deleted:Īs we can see, the records have been deleted and the table returns an empty set. To delete all the records from the “Employee_details” table: The syntax of this command is:Īs we can see, there is no ‘WHERE’ clause, so this command is used only when we need to empty the contents of a table. This is a part of the Data Definition Language, a sub-language of SQL that allows the creation and modification of database objects. We can also use the TRUNCATE command to delete all the records from a table.To check whether all the records are deleted, we’ll use the SELECT command:Īs we can see, the SELECT command returns an empty set as all the records from the “Employee_details” table have been deleted. To delete all the records from our “Employee_details” table, we’ll use the following query: If not done intentionally, this could cause a lot of problems. Without a WHERE clause, all the records of the table are deleted.It’s imperative to be extremely careful while using the DELETE command on a table as the data gets deleted permanently. More than one condition can be applied to the columns using a single query. We can also delete multiple rows using a single query.įrom the table displayed above, we need to delete all the employee records with salary less than 60000:Īs we can see, four rows have been deleted.The query above will result in the following: From the table above, we need to delete the record of the employee with the name “Arun”:Īs we can see, “Name” is of character string data type, so the value being specified has to be enclosed in single inverted commas, without which the system will return a syntax error.To check the result of the query in the table above, we’ll use the ‘SELECT *’ command:Īs we can see, one record has been deleted based on the condition specified in the WHERE clause.From the table depicted above, to delete the employee’s record with “EmployeeID” equal to one, we’ll use the following query:.Let’s take a sample “Employee_details” table Deleting Specific Rows Based on a Single Condition Let’s apply the concepts stated above to the rows of a table. Multiple conditions can be specified in the WHERE clause with the help of AND and OR operators. ![]() NOTE: Extra caution needs to be taken with the WHERE clause as, without it, all the rows from the table will get deleted.
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