51 lines
1.7 KiB
Markdown
51 lines
1.7 KiB
Markdown
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# DELETE
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## Overview
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The `DELETE` statement is fundamental for data management, enabling the removal of rows from a database table. Proper use ensures data integrity and efficiency within your application's data layer.
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## Basic DELETE
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Removes specific rows based on a condition. The `WHERE` clause is critical for precise targeting. Omitting it will affect all rows in the table.
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```sql
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DELETE FROM users WHERE id=5;
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```
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A successful operation indicates the number of rows removed.
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```
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Query OK, 1 row affected (0.01 sec)
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```
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## Critical Warning
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Executing `DELETE` without a `WHERE` clause removes all data from the specified table.
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```sql
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DELETE FROM users;
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```
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Output reflects the total count of rows deleted.
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```
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Query OK, x row(s) affected (0.047 sec)
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```
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Unlike operations within a transaction that can be rolled back, standard `DELETE` operations are permanent. Recovery typically requires restoring from a backup.
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## Deleting Based on Related Tables
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Rows can be deleted from one table based on criteria evaluated against another table. This commonly involves using `JOIN` clauses within the `DELETE` statement to link related data. While the `FROM` clause may reference multiple tables, the `DELETE` clause specifies only the table from which rows are removed.
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For instance, to remove users from the `users` table if their corresponding entry in `prospect_users` is marked inactive:
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```sql
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delete users
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from users, prospect_users
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where users.username = prospect_users.username
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and NOT prospect_users.active;
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```
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This approach efficiently removes dependent data, maintaining data consistency across related tables.
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