SQL DELETE — deleting all rows in a table To remove all rows in the employees table, you just execute the following query: not recommended and make a backup before you do this. SQL DELETE — deleting related rows in multiple tables It becomes more complicated when you want to delete a row in a table that is associated with other rows in another table. For example, each employee is working in one or more territories and each territory has multiple employees. The employeeterritories table is used to store relationships between employees and territories.
When you remove a row in the employees table, you must also remove the related rows in the employeeterritories table. Most database management systems allow you to create a foreign key constraint so that if you delete a row in a table, the corresponding rows the related table are also removed automatically.
This ensures the integrity of the data. In case the database management system does not support the foreign key constraint, you have to execute both DELETE statements in a single transaction to make sure that the statements execute in all-or-nothing mode.
ZenTut Programming Made Easy. Was this tutorial helpful? Yes No.MySQL Tutorial for Beginners - 5 - Deleting Data From a Database
Return to top of page. All Rights Reserved.MySQL should need no introduction. It is the power behind most websites that run WordPress or many custom CMS and the engine behind many a company database. It is a simple but very effective system that makes managing and storing data very straightforward once you know how.
Today we are going to cover how create and delete tables in MySQL. Tables are collections of related data structured in a logical way. Tables use rows and columns to order data values in cells. Each table has a unique name. Each column will have a name, data type and any other attributes relevant to the column. Rows will also have names and will contain data relevant to the columns. I shall walk you through creating and deleting tables in MySQL. You will likely find that you gravitate towards the GUI or queries.
There is no right way or best way, use what you feel most comfortable with. Be aware that deleting a table is permanent. SQL does not keep copies or save files to protect data. Unless you have taken a backup of your database, there is no going back. It might be a good idea to take that backup before you start creating and deleting tables.
Here is how create and delete tables in MySQL using queries. This would create a table if it did not already exist and auto increment each row with an ID number while creating columns for the last name, first name and their join date.
You can create and delete tables in SQL with very little effort. Sometimes too little effort! You can also use a PHP file for creating databases, tables and entries in one go and I will cover that another time. Some purists say you should always use queries to perform actions in databases and there is sense in that.
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Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. You can use the below query to remove all the rows from the table, also you should keep it in mind that it will reset the Identity too.
You should be fine with truncate though:. There is a mySQL bug report from that still seems to have some validity. It seems that in 4. Learn more. Asked 9 years, 10 months ago. Active 4 months ago.
Viewed k times. For what database? For what table? For what size of data? What did you find out when you measured the time taken by both? I found someone accidentally put this in code, and was searching to see how common it was. I also made a test table and sure enough, no joy with the asterisk. This question is a mess, because it has accumulated answers both for [mysql] and [ms-access].
Active Oldest Votes. Vignesh Kumar A Jaymz Jaymz 5, 1 1 gold badge 23 23 silver badges 29 29 bronze badges. No, would have helped if you mentioned Access in your original question.
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No, it's not supported in Access. I don't think it resets the Autonumber seed value, though. I can confirm that if all records are deleted from an Access table, a Compact will reset the Autonumber seed value in Access Replace it with the name of the table, which shall be deleted.
Altay Akkus 10 10 bronze badges. Oladimeji Ajeniya Oladimeji Ajeniya 3 3 silver badges 8 8 bronze badges.Note: Be careful when deleting records in a table! It is possible to delete all rows in a table without deleting the table. This means that the table structure, attributes, and indexes will be intact:. The following SQL statement deletes all rows in the "Customers" table, without deleting the table:. Delete all the records from the Customers table where the Country value is 'Norway'.
If you want to report an error, or if you want to make a suggestion, do not hesitate to send us an e-mail:. Exercise: Delete all the records from the Customers table where the Country value is 'Norway'.
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That will drop the table only if it contains any rows and will raise an error if the table does not exist. See the answer by Jovan. Have seen so many that don't really work. TableName is your desired table and 'U' is type of your table. Select and Right Click the Table you wish to delete, then delete. Such a screen should be displayed. Click Update Database to confirm.
This method is very safe as it gives you the feedback and will warn of any relations of the deleted table with other tables. Learn more.
Drop a Table
How to drop a table if it exists? Ask Question. Asked 8 years, 5 months ago. Active 1 month ago. Viewed 1. The table name is Scores. Is it correct to do the following?
Alexander Abakumov 8, 6 6 gold badges 57 57 silver badges 93 93 bronze badges. Active Oldest Votes. Scores No. Palec 9, 6 6 gold badges 49 49 silver badges 99 99 bronze badges.
Martin Smith Martin Smith k 71 71 gold badges silver badges bronze badges. Fwiw -- The 'U' for the second param apparently means "Only look for objects with this name that are tables". One source. Regarding the second param; here is another sourceI used 'V' for a View. T', 'U'for example this 'U'? ZvonimirTokic it means "User defined Table". A full list is here msdn. Callum Watkins 2, 2 2 gold badges 22 22 silver badges 38 38 bronze badges. Is the if exists ansi compliant? Be careful if you have more than one schema in the database.
You might need to be specific about which [Scores] you are detecting and deleting.You can delete drop a table from your database in SQL Server Think carefully before you delete a table. If existing queries, views, user-defined functions, stored procedures, or programs refer to that table, the deletion will make these objects invalid.
When a table is dropped, rules or defaults on the table lose their binding, and any constraints or triggers associated with the table are automatically dropped. If you re-create a table, you must rebind the appropriate rules and defaults, re-create any triggers, and add all required constraints. Otherwise an unexpected error may occur.
Any view or stored procedure that references the dropped table must be explicitly deleted or modified to remove the reference to the table. You may also leave feedback directly on GitHub. Skip to main content.
Exit focus mode. Caution Think carefully before you delete a table. Note Deleting a table automatically removes any relationships to it. Is this page helpful? Yes No. Any additional feedback? Skip Submit. Send feedback about This product This page. This page. Submit feedback. There are no open issues. View on GitHub.For an external table, this statement removes only the table metadata in the database.
It has no affect on the actual data, which resides outside of the database. When you drop a table that is part of a cluster, the table is moved to the recycle bin. Dropping a table invalidates dependent objects and removes object privileges on the table. If you want to re-create the table, then you must regrant object privileges on the table, re-create the indexes, integrity constraints, and triggers for the table, and respecify its storage parameters. Truncating has none of these effects.
Specify the schema containing the table. If you omit schemathen Oracle Database assumes the table is in your own schema. Specify the name of the table to be dropped. Oracle Database automatically performs the following operations:. All table indexes and domain indexes are dropped, as well as any triggers defined on the table, regardless of who created them or whose schema contains them.
If table is partitioned, then any corresponding local index partitions are also dropped. All the storage tables of nested tables and LOBs of table are dropped. When you drop a range- hash- or list-partitioned table, then the database drops all the table partitions.
Delete Tables (Database Engine)
If you drop a composite-partitioned table, then all the partitions and subpartitions are also dropped. When you drop a partitioned table with the PURGE keyword, the statement executes as a series of subtransactions, each of which drops a subset of partitions or subpartitions and their metadata. This division of the drop operation into subtransactions optimizes the processing of internal system resource consumption for example, the library cacheespecially for the dropping of very large partitioned tables.
PURGE statement. Such a statement will resume work from where the previous DROP TABLE statement failed, assuming that you have corrected any errors that the previous operation encountered. For an index-organized table, any mapping tables defined on the index-organized table are dropped.
For a domain index, the appropriate drop routines are invoked. If any statistic types are associated with the table, then the database disassociates the statistics types with the FORCE clause and removes any user-defined statistics collected with the statistics type.
If the table is not part of a cluster, then the database returns all data blocks allocated to the table and its indexes to the tablespaces containing the table and its indexes. If the table is a base table for a view, a container or master table of a materialized view, or if it is referenced in a stored procedure, function, or package, then the database invalidates these dependent objects but does not drop them.
You cannot use these objects unless you re-create the table or drop and re-create the objects so that they no longer depend on the table. If you choose to re-create the table, then it must contain all the columns selected by the subqueries originally used to define the materialized views and all the columns referenced in the stored procedures, functions, or packages. Any users previously granted object privileges on the views, stored procedures, functions, or packages need not be regranted these privileges.
If the table is a master table for a materialized view, then the materialized view can still be queried, but it cannot be refreshed unless the table is re-created so that it contains all the columns selected by the defining query of the materialized view.
If the table has a materialized view log, then the database drops this log and any other direct-path INSERT refresh information associated with the table.