SQL WHERE clause
WHERE clause is used to filter the records.
SQL WHERE clause
WHERE clause is used to extract records that meet the specified criteria.
SQL WHERE Syntax
SELECT column_name , column_name
FROM table_name
WHERE column_name operator value ;
FROM table_name
WHERE column_name operator value ;
The demo database
In this tutorial, we will use w3big sample database.
The following is a selected "Websites" table data:
+----+--------------+---------------------------+-------+---------+ | id | name | url | alexa | country | +----+--------------+---------------------------+-------+---------+ | 1 | Google | https://www.google.cm/ | 1 | USA | | 2 | 淘宝 | https://www.taobao.com/ | 13 | CN | | 3 | 本教程 | http://www.w3big.com/ | 4689 | CN | | 4 | 微博 | http://weibo.com/ | 20 | CN | | 5 | Facebook | https://www.facebook.com/ | 3 | USA | +----+--------------+---------------------------+-------+---------+
WHERE clause examples
The following SQL statement Select a country as "CN" from all the sites "Websites" table:
Examples
SELECT * FROM Websites WHERE country = 'CN';
Execution output:
Text field vs. a numeric field
SQL uses single quotes to surround text values (most database systems also accept double quotes).
In the last instance 'CN' text field uses a single quote.
If it is a numeric field, do not use quotation marks.
Examples
SELECT * FROM Websites WHERE id = 1;
Execution output:
WHERE clause operator
The following operators can use in the WHERE clause:
| Operators | description |
|---|---|
| = | equal |
| <> | not equal to.NOTE: In some versions of SQL, the operator can be written as =! |
| > | more than the |
| < | Less than |
| > = | greater or equal to |
| <= | Less than or equal |
| BETWEEN | Within a certain range |
| LIKE | Search for a pattern |
| IN | Specifies the possible values for a plurality of columns |