MySQL Examples. This page contains MySQL examples, including sample scripts for installing a DB, inserting data, running queries, and more. Most examples linked to from this page use the Sakila sample database. Installs the 'Sakila' sample database complete with thousands of rows of data.
What is the DELETE Keyword? The SQL DELETE command is used to delete rows that are no longer required from the database tables. It deletes the whole row from the table. Delete command comes in handy to delete temporary or obsolete data from your database.The DELETE command can delete more than one row from a table in a single query.
This proves to be advantages when removing large numbers of rows from a database table. Once a row has been deleted, it cannot be recovered.
It is therefore strongly recommended to make database backups before deleting any data from the database. This can allow you to restore the database and view the data later on should it be required. Delete command syntax The basic syntax of the delete command is as shown below. INSERT INTO `movies` (`title`, `director`, `yearreleased`, `categoryid`) VALUES ('The Great Dictator', 'Chalie Chaplie', 1920, 7); INSERT INTO `movies` (`title`, `director`, `categoryid`) VALUES ('sample movie', 'Anonymous', 8); INSERT INTO movies (`title`, `director`, `yearreleased`, `categoryid`) VALUES ('movie 3', 'John Brown', 1920, 8); Executing the above script adds three (3) movies into the movies table. Before we go any further into our lesson, let's get all the movies in our table. The script shown below does that.
SELECT. FROM `movies`; Executing the above script gives us the following results.
SELECT. FROM `movies`; movieid title director yearreleased categoryid 1 Pirates of the Caribean 4 Rob Marshall 2011 1 2 Forgetting Sarah Marshal Nicholas Stoller 2008 2 3 X-Men NULL 2008 NULL 4 Code Name Black Edgar Jimz 2010 NULL 5 Daddy's Little Girls NULL 2007 8 6 Angels and Demons NULL 2007 6 7 Davinci Code NULL 2007 6 9 Honey mooners John Schultz 2005 8 16 67% Guilty NULL 2012 NULL 19 sample movie Anonymous NULL 8 20 movie 3 John Brown 1920 8 NOTE:.
the movie with id 18 has not been return in the query result set. you cannot delete a single column for a table. You can delete an entire row. Let's say we have a list of movies we want to delete. We can use the WHERE clause along with IN. UPDATE `tablename` SET `columnname` = `newvalue' WHERE condition; HERE.
UPDATE `tablename` is the command that tells MySQL to update the data in a table. SET `columnname` = `newvalue' are the names and values of the fields to be affected by the update query. Note, when setting the update values, strings data types must be in single quotes. Numeric values do not need to be in quotation marks. Date data type must be in single quotes and in the format 'YYYY-MM-DD'. WHERE condition is optional and can be used to put a filter that restricts the number of rows affected by the UPDATE query. Let's now look at a practical example that updates data in the members table.
Let's suppose that our member's membership numbers 1 and 2 have the following updates to be made to their data records. Membership number Updates required 1 Changed contact number from 999 to 0759 253 532 2 Change the name to Janet Smith Jones and physical address should be updated to Melrose 123 We will start with making updates for membership number 1 before we make any updates to our data, let's retrieve the record for membership number 1. The script shown below helps us to do that. SELECT. FROM `members` WHERE `membershipnumber` = 1; Executing the above script gives us the following results.
Membershipnumber fullnames gender dateofbirth physicaladdress postaladdress contctnumber email 1 Janet Jones Female First Street Plot No 4 Private Bag 0759 253 542 This email address is being protected from spambots. You need JavaScript enabled to view it.
Let's now look at the updates required for membership number 2. Membershipnumber fullnames gender dateofbirth physicaladdress postaladdress contctnumber email 2 Smith Jones Female Park Street NULL NULL This email address is being protected from spambots. You need JavaScript enabled to view it. The following script helps us to do that.
UPDATE `members` SET `fullnames` = 'Janet Smith Jones', `physicaladdress` = 'Melrose 123' WHERE `membershipnumber` = 2; Executing the above script in updates the full names for membership number 2 to Janet Smith Jones and the physical address to Melrose 123. Membershipnumber fullnames gender dateofbirth physicaladdress postaladdress contctnumber email 2 Janet Smith Jones Female Melrose 123 NULL NULL This email address is being protected from spambots.
You need JavaScript enabled to view it. Summary. The delete command is used to remove data that is no longer required from a table. The 'WHERE clause' is used to limit the number of rows affected by the DELETE query. Once data has been deleted, it cannot be recovered, it is therefore strongly recommend make backups before deleting data. The update command is used to modify existing data.
The 'WHERE clause' is used to limit the number of rows affected by the UPDATE query.