WHERE 子句过滤各种语句,如SELECT,UPDATE,DELETE和INSERT.它们提供了用于指定行动的标准.它们通常出现在语句中的表名之后,其条件如下. WHERE子句的功能基本上类似于if语句.
查看下面给出的WHERE子句的一般语法 :
[COMMAND] field,field2,... FROM table_name,table_name2,... WHERE [CONDITION]
注意WHERE的以下特性子句 : 去;
这是可选的.
它允许指定任何条件.
它允许通过使用AND或OR运算符来指定多个条件.
区分大小写仅适用于使用LIKE比较的语句.
WHERE子句允许使用以下运算符 :
运算符 |
---|
=!= |
> < |
> =< = |
可以在命令提示符或PHP脚本中使用WHERE子句.
在命令提示符下,只需使用标准命令 :
root@host# mysql -u root -p password; Enter password:******* mysql> use PRODUCTS; Database changed mysql> SELECT * from products_tbl WHERE product_manufacturer = 'XYZ Corp'; +-------------+----------------+----------------------+ | ID_number | Nomenclature | product_manufacturer | +-------------+----------------+----------------------+ | 12345 | Orbitron 4000 | XYZ Corp | +-------------+----------------+----------------------+ | 12346 | Orbitron 3000 | XYZ Corp | +-------------+----------------+----------------------+ | 12347 | Orbitron 1000 | XYZ Corp | +-------------+----------------+----------------------+
使用 AND 条件 :
SELECT * FROM products_tbl WHERE product_name = 'Bun Janshu 3000'; AND product_id <= 344;
此示例结合了AND和OR条件
SELECT * FROM products_tbl WHERE (product_name = 'Bun Janshu 3000' AND product_id < 344) OR (product_name = 'Bun Janshu 3000');
在操作中使用 mysql_query()函数一个WHERE子句 :
<?php $dbhost = 'localhost:3036'; $dbuser = 'root'; $dbpass = 'rootpassword'; $conn = mysql_connect($dbhost, $dbuser, $dbpass); if(! $conn ) { die('Could not connect: ' . mysql_error()); } $sql = 'SELECT product_id, product_name, product_manufacturer, ship_date FROM products_tbl WHERE product_manufacturer = "XYZ Corp"'; mysql_select_db('PRODUCTS'); $retval = mysql_query( $sql, $conn ); if(! $retval ) { die('Could not get data: ' . mysql_error()); } while($row = mysql_fetch_array($retval, MYSQL_ASSOC)) { echo "Product ID :{$row['product_id']} <br> ". "Name: {$row['product_name']} <br> ". "Manufacturer: {$row['product_manufacturer']} <br> ". "Ship Date: {$row['ship_date']} <br> ". "--------------------------------<br>"; } echo "Fetched data successfully\n"; mysql_close($conn); ?>
成功检索数据后,您将看到以下输出 :
Product ID: 12345 Nomenclature: Orbitron 4000 Manufacturer: XYZ Corp Ship Date: 01/01/17 ---------------------------------------------- Product ID: 12346 Nomenclature: Orbitron 3000 Manufacturer: XYZ Corp Ship Date: 01/02/17 ---------------------------------------------- Product ID: 12347 Nomenclature: Orbitron 1000 Manufacturer: XYZ Corp Ship Date: 01/02/17 ---------------------------------------------- mysql> Fetched data successfully