Quelle est la syntaxe de l’instruction SQL DELETE ?

The DELETE statement is used to remove records from a database table. The basic syntax is generally similar across different databases, but there can be variations in capabilities and specific syntax. Here are examples for a few popular relational database management systems: MySQL, SQL Server, SQLite: DELETE FROM customers WHERE customer_id = 10; PostgreSQL: DELETE FROM customers WHERE customer_id = 10 RETURNING *; Oracle supports the RETURNING clause like PostgreSQL, which can be used for returning values from the deleted rows.

I'll add in a little trick I like: select * --delete from table_name where condition_exists You can run this whole script and it will only select the data that fulfills the where condition which, in essence, gives you a preview of what you're about to delete. When you're ready to perform the delete, highlight the script manually from 'delete' onwards (omitting the in-line comment --).

when using the delete statement, one has to be aware of conflicting a reference constraint. This arises when the data you are trying to delete is referenced by another tuple existing in another relation.

Additionally, it is crucial to exercise caution when using the DELETE statement, as it permanently removes data. It is advisable to back up the information before executing the statement and ensure that the condition in the WHERE clause is precise to avoid unnecessary losses. Moreover, in production environments, testing in development environments before applying the DELETE statement is advisable. This helps prevent potential issues and ensures secure database management.

Running a delete statement on production always gives me an adrenaline spike. Good practice to do a select first with your condition and make sure you have a backup or temp table in place

The DELETE statement, while powerful, has some limitations. In large-scale environments, its indiscriminate use can impact database performance. Additionally, when deleting records, it's crucial to consider foreign key relationships, as improper handling can lead to inconsistencies in referential integrity. Understand the limitations of DELETE to optimize its application and avoid unintended impacts on the database.

I agree, but to highlight the versatility and power of SQL beyond the basic DELETE statement, emphasizes the importance of performance considerations. When deleting large amounts of data it is often more efficient to create a new table with the data you want to keep, and then rename the new table to the old one. This can be faster than deleting rows one by one. ```SQL SELECT * temp_customers FROM customers WHERE name NOT LIKE 'A%' AND name NOT LIKE 'B%'; DROP TABLE customers; EXEC sp_rename 'temp_customers', 'customers'; ``` Stay vigilant!

The SQL Delete statement should be update to only execute with a "Where Clause" at all times and maybe add a "With" so that the deleted record can either be logged or archived. e.g. delete from products where pid=0 with log/archieve. in this way no record which enter the database will be lost. I had experience where production records where deleted without warning or possibility of rollback on SQL Server.

Example 1: DELETE FROM Customers WHERE CustomerID = 1; This command deletes a specific record in the Customers table where CustomerID equals 1. If CustomerID is unique, it removes one row; otherwise, it deletes all rows with CustomerID 1. Caution: It's irreversible, and recovery is possible only through a backup. Example 2: DELETE FROM Customers; This command removes all records from the Customers table. There's no WHERE clause, meaning it applies to all rows. Caution: This is a significant and irreversible action. Ensuring it's the desired action and having backups or safeguards against accidental data loss is crucial.

If you want delete all rows, the best option and the fastest is Truncate the table. This action cant be undone, so you must be really sure of this. Example: TRUNCATE TABLE <TableName>

Quando uma instrução DELETE é executada, o query optmizer gera um plano de execução para instrução (baseado nas estatísticas coletada pelo banco de dados), porém diversas outras atividades são realizadas pelo SGBD. Alguns fatores podem afetar o locking e o desempenho da exclusão do comando, como por exemplo: - Triggers - Muitos índices na tabela - Chaves estrangeiras com índices inadequados - Lock mode - Tamanho do lote de registros afetado pela instrução

This is not exactly a limitation but what I believe is the correct way to run any DELETE command if you are a newbie to SQL. Always try SELECTing the data you want to DELETE. This way you can be sure that the WHERE clause is inclusive of only what you want to remove and not any other useful information.

Exploring alternatives to the SQL DELETE statement can be crucial in certain contexts. Consider using operations like UPDATE or MERGE to modify data instead of completely deleting it. Additionally, creating history tables or implementing timestamp markers can be an effective strategy for tracking changes without losing valuable information. Evaluating these alternatives provides greater flexibility and control in data management within your database

The DELETE statement cannot delete specific columns, only entire rows. Without a WHERE clause, it removes all rows from the table, which can be irreversible if not handled carefully. It does not automatically reclaim the space used by the deleted rows.

La commande DELETE n'est pas équivalente à marquer un champs à inactif, à détruire une table ou la vider. De même pour le CASCADE, il faudra se montrer prudent car cela supprime en premier toutes les dépendances filles et si l'auto COMMIT est à ON alors en cas de ROLLBACK de la dernière commande, les filles seront perdues.

Drop, Delete and Truncate commands are often confused. Drop - Delete entire table. Cannot be rolled back. While using this we should check the constraints of the table else we can encounter error while execution. Delete - Delete single/multiple/all rows in a table. Can be rolled back. Truncate - Delete all rows in table. Cannot be rolled back. Always its a best practice to use transactions while writing a big delete/update command. So in case any of the queries fail the changes will not be appiled to the DB. Also its good to use select query to check the rows that would be impacted. In case you are using a backup DB then make sure that your record is inserted to the backup table and post that you execute the delete command.

Alternatives to the SQL DELETE statement offer diverse approaches for managing data within a table. The SQL UPDATE statement, for instance, allows you to modify column values without deleting rows. For instance, to mark rows with null email columns as inactive, use the following statement: ```sql UPDATE customers SET status = 'inactive' WHERE email IS NULL; ``` This statement updates the status column to "inactive" for rows where the email column is null. Another option is the SQL DROP statement, which removes an entire table along with its structure and indexes. This can be beneficial when you no longer need a table. For example, to delete the customers table, you can use: ```sql DROP TABLE customers; ``

TRUNCATE TABLE: Swiftly clears all rows from a table, faster than DELETE without a WHERE clause, but irreversible. E.g., TRUNCATE TABLE customers;. UPDATE: Alters column values without row deletion, ideal for status changes. E.g., UPDATE customers SET status = 'inactive' WHERE email IS NULL;. Soft Delete: Uses a column like is_deleted to flag rows as deleted, keeping data while allowing 'undo'. E.g., UPDATE customers SET is_deleted = 1 WHERE condition;. Each method serves different needs. An alternative approach is suitable for small tables but can slow down large tables and increase storage costs, as data stays in the table, affecting space and performance.

Podem ser pensadas alternativas para o DELETE que possibilitam ações que resolveriam a situação enfrentada. Ex: Ao invés de deletar uma linha inteira por um campo estar desatualizado, pode-se utilizar um UPDATE (que também faz parte do grupo de DML) afim de preencher ou atualizar a informação errada. Também pode-se, em caso em que se faria necessário a exclusão de muitas linhas de um banco muito grande, (o que seria um problema de performance) fazer um backup da tabela (para ter um esqueleto na hora de recria-la melhorada) e utilizar um DROP (que faz parte do conjunto DDL) TABLE a fim de que toda a tabela com suas informações e índices sejam deletados do banco.

truncate is also very useful as it frees up the tablespace. I always use it on staging tables on interfaces that move data from one place to another (also incorporating transformation as appropriate). These tables are used for a set of operations and then left filled until the interface runs again, at which point the tables are truncated. This also leaves the records in the tables between interface runs which means you can see what was interfaced

Avant tout suppression (DELETE) ou modification de données (INSERT UPDATE) s assurer que l on est en mode transactionnel (BEGIN TRAN ou avoir AUTO COMMITED désactivé) de manière à pouvoir effectuer un ROLLBACK en cas d erreur.

I've used the SQL DELETE command for precise data removal, adapting it to specific requirements. For example, I've used the DELETE FROM table WHERE condition to remove rows based on precise criteria while minimizing the impact on database integrity. However, I've discovered certain limits, such as inefficiency with large datasets. In such circumstances, alternatives such as TRUNCATE proven more effective for large-scale deletions. Furthermore, knowing the DELETE statement's possible impact on database performance has been critical, especially in transaction-intensive situations. In my professional experience, effectively managing databases has required balancing its use with other commands such as UPDATE or DROP, depending on the scenario.

It is necessary to mention some important considerations and precautions when using the DELETE statement: the irreversible nature of data deletion and the importance of being cautious with the WHERE clause to avoid unintentional data loss.

When using DELETE you have to take care of referential integrity. For example, if you have DB with tables: "person" and "city" and relation of person and his hometown (via referential integrity) you can't delete city that has at least one person born in it. You can do a cascade delete (not recommended) that will delete city and also all persons born in that city. Deleting one record you will delete maybe other records (information), that You don't want to lose. Third option is to keep Person record (while deleting city) and to set his hometown (that will be deleted) to NULL (partial loss of information). To summarize You can: 1. forbid deletion; 2. on delete cascade 3. on delete update to null (some information will be lost but not all)

Como dito acima, o comando DELETE pode ser muito útil, embora perigoso caso feito de forma desatenta. Treinem muito o delete, com suas particularidades e capacidades.

In a partitioned table by a specific column If you want to delete all rows with that column=X, you can truncate the relating partition. It will be faster than "delete from table where column=X"

In some scenarios, you might need to delete records from one table based on a condition involving another table. This can be achieved using the DELETE statement with a JOIN. Syntax: Delete t1 FROM table1 t1 JOIN table2 t2 on t1.column_name =t2.column_name where t2.some_condition;

Always keep in mind the necessary permissions required. Everyone who can query data, should not be given access to be able to delete it as well (as it can lead to losing data)

Before using SQL commands that are final, regardless of whether you have a backup, steal from Delicious Brains and do a "Dry Run". Use the SELECT command first. Sure you're sure you need to delete customer ID 42 from the database, but one extra step before a DELETE, DROP, or even an UPDATE might show some anomaly where you were about to delete more rows than you bargained for. Also, why not use a staging or local build to test rather than running SQL commands in Production?

You can also have triggers that will save data on deletion in some other archive table just to be sure what was deleted, when etc. At the beginning of my carrier, I had interesting case when customer was firmly stating that he didn't delete data from DB, via application. It was a payroll system and people are very sensitive on errors there. This deletion could cause error in calculations. Fortunately, I had a record in archive table: what was deleted, when was deleted and by whom ;). That trigger and archive table really saved me back than :) because client never confessed that he did delete previous month payroll data.