SQL DELETE statement

The DELETE statement is used to delete records in a table.

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SQL DELETE statement

The DELETE statement is used to delete rows in a table.

SQL DELETE syntax

DELETE FROM table_name
WHERE some_column=some_value;

	Note the WHERE clause in the SQL DELETE statement!  The WHERE clause specifies which records or which records need to be deleted. If you omit the WHERE clause, all the records will be deleted!

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Demo database

In this tutorial, we will use the RUNOOB sample database.

The following is the data selected from the "Websites" table:

+ ---- + -------------- + --------------------------- + - ------ + --------- + | id | name          | url                        | alexa | country | + ---- + -------------- + - -------------------------- + ------- + --------- + | 1 | Google | Https : //www.google.cm/ | 1 | USA | | 2 | Taobao | https : //www.taobao.com/ | 13 | CN | | 3 | Rookie Tutorial | http : //www.runoob.COM / | 4689 | CN | | 4 | Twitter | HTTP : //weibo.com/ | 20 | CN | | 5 | Facebook | HTTPS : //www.facebook.com/ | 3 | USA | | 6 | Baidu | Https : //www.baidu.com/ | 4 | CN | | 7 | stackoverflow | http : //stackoverflow.com/ | 0 | IND | + ---- + ---------- ----- + --------------------------- + ------- + -------- - +COM / | 20 is | the CN | | . 5 | Facebook | HTTPS : //www.facebook.com/ |. 3 | USA | | . 6 | Baidu | HTTPS : //www.baidu.com/ |. 4 | the CN | | . 7 | Stackoverflow | http : //stackoverflow.com/ | 0 | IND | + ---- + --------------- + ------------- -------------- + ------- + --------- +COM / | 20 is | the CN | | . 5 | Facebook | HTTPS : //www.facebook.com/ |. 3 | USA | | . 6 | Baidu | HTTPS : //www.baidu.com/ |. 4 | the CN | | . 7 | Stackoverflow | http : //stackoverflow.com/ | 0 | IND | + ---- + --------------- + ------------- -------------- + ------- + --------- +Com | | 4 | CN | | 7 | stackoverflow | http : //stackoverflow.com/ | 0 | IND | + ---- + --------------- + --- ------------------------ + ------- + --------- +Com | | 4 | CN | | 7 | stackoverflow | http : //stackoverflow.com/ | 0 | IND | + ---- + --------------- + --- ------------------------ + ------- + --------- +


           
              
          
              
         
             
   

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SQL DELETE instance

Suppose we want to remove the site from the "Websites" table named "Baidu" and the country for the CN site.

We use the following SQL statement:

Examples

DELETE FROM Websites WHERE name = ' Baidu ' AND country = ' CN ' ;

Execute the above SQL, and then read the "Websites" table, the data is as follows:

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Delete all data

You can delete all the rows in the table without deleting the table. This means that the table structure, attributes, and indexes will remain the same:

DELETE FROM table_name ;

or

DELETE * FROM table_name ;

Note: Be careful when deleting records! Because you can not come back!

SQL UPDATE statement

The UPDATE statement is used to update the records in the table.

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SQL UPDATE statement

The UPDATE statement is used to update an existing record in the table.

SQL UPDATE syntax

UPDATE table_name
SET column1 = value1 , column2 = value2 ,...
WHERE some_column = some_value ;

	Note the WHERE clause in the SQL UPDATE statement! The WHERE clause specifies which records or which records need to be updated. If you omit the WHERE clause, all the records will be updated!

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Demo database

In this tutorial, we will use the RUNOOB sample database.

The following is the data selected from the "Websites" table:

 + ---- + -------------- + --------------------------- + - ------ + --------- +
 | Id | name | url | alexa | country |
 + ---- + -------------- + --------------------------- + - ------ + --------- +
 | 1 | Google | https://www.google.cm/ | 1 | USA |
 | 2 | Taobao | https://www.taobao.com/ | 13 | CN |
 | 3 | rookie tutorial | http://www.runoob.com/ | 4689 | CN |
 | 4 | microblogging | http://weibo.com/ | 20 | CN |
 5 | Facebook | https://www.facebook.com/ | 3 | USA |
 + ---- + -------------- + --------------------------- + - ------ + --------- +

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SQL UPDATE instance

Suppose we want to update the "rookie tutorial" alexa ranking to 5000, country changed to USA.

We use the following SQL statement:

Examples

UPDATE Websites SET Alexa = ' 5000 ' , country = ' USA ' WHERE Name = ' rookie tutorial ' ;

Execute the above SQL, and then read the "Websites" table, the data is as follows:

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Update Warning!

Be extra careful when updating your records! In the above example, if we omit the WHERE clause, as follows:

UPDATE Websites
SET alexa = '5000', country = 'USA' 

The above code will change all the data in the Websites table alexa to 5000, country to USA.

Execute UPDATE without WHERE clause to be careful and cautious.

SQL ORDER BY keyword

The ORDER BY keyword is used to sort the result set.

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SQL ORDER BY keyword

The ORDER BY keyword is used to sort the result set by a column or columns.

The ORDER BY keyword sorts the records by default. If you need to sort the records in descending order, you can use the DESC keyword.

SQL ORDER BY syntax

SELECT column_name , column_name
FROM table_name
ORDER BY column_name , column_name ASC|DESC;

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Demo database

In this tutorial, we will use the RUNOOB sample database.

The following is the data selected from the "Websites" table:

 + ---- + -------------- + --------------------------- + - ------ + --------- +
 | Id | name | url | alexa | country |
 + ---- + -------------- + --------------------------- + - ------ + --------- +
 | 1 | Google | https://www.google.cm/ | 1 | USA |
 | 2 | Taobao | https://www.taobao.com/ | 13 | CN |
 | 3 | rookie tutorial | http://www.runoob.com/ | 4689 | CN |
 | 4 | microblogging | http://weibo.com/ | 20 | CN |
 5 | Facebook | https://www.facebook.com/ | 3 | USA |
 + ---- + -------------- + --------------------------- + - ------ + --------- +

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ORDER BY instance

The following SQL statement selects all sites from the "Websites" table and sorts them according to the "alexa" column:

Examples

SELECT * FROM Websites ORDER BY Alexa

Execute the output:

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ORDER BY DESC instance

The following SQL statement selects all sites from the "Websites" table and sorts them in descending order of "alexa"

Examples

SELECT * FROM Websites ORDER BY Alexa DESC ;

Execute the output:

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ORDER BY multiple columns

The following SQL statement selects all sites from the "Websites" table and sorts them according to the "country" and "alexa" columns:

Examples

SELECT * FROM Websites ORDER BY Country , alexa

Execute the output:

SQL AND & OR operator

The AND & OR operator is used to filter records based on more than one condition.

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SQL AND & OR operator

If both the first condition and the second condition are true, the AND operator displays a record.

If only one of the first condition and the second condition holds, the OR operator displays a record.

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Demo database

In this tutorial, we will use the RUNOOB sample database.

The following is the data selected from the "Websites" table:

+ ---- + -------------- + --------------------------- + - ------ + --------- + | id | name          | url                        | alexa | country | + ---- + -------------- + - -------------------------- + ------- + --------- + | 1 | Google | Https : //www.google.cm/ | 1 | USA | | 2 | Taobao | https : //www.taobao.com/ | 13 | CN | | 3 | Rookie Tutorial | http : //www.runoob.COM / | 4689 | CN | | 4 | Twitter | HTTP : //weibo.com/ | 20 | CN | | 5 | Facebook | HTTPS : //www.facebook.com/ | 3 | USA | + --- - + -------------- + --------------------------- + ----- - + --------- +


           
              
          
              
         

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AND operator instance

The following SQL statement selects all sites from the "Websites" table for "CN" and alexa rank greater than "50":

Examples

SELECT * FROM Websites WHERE country = ' CN ' AND alexa > 50 ;

Execute the output:

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OR operator instance

The following SQL statement selects all customers whose country is "USA" or "CN" from the "Websites" table:

Examples

SELECT * FROM Websites WHERE country = ' USA ' OR country = ' CN ' ;

Execute the output:

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Combined with AND & OR

You can also combine AND and OR (using parentheses to form complex expressions).

The following SQL statement selects all sites with alexa rank greater than "15" and "CN" or "USA" from the "Websites" table:

Examples

SELECT * FROM Websites WHERE alexa > 15 AND ( country = ' CN ' OR country = ' USA ' ) ;

Execute the output: