MariaDB Where 子句怎么用？筛选数据条件查询全解析？

WHERE子句用于过滤 SELECT、UPDATE、DELETE 和 INSERT 等各种语句。它们呈现用于指定操作的条件。通常在语句中的表名之后出现其条件紧随其后。WHERE 子句本质上类似于 if 语句。查看以下 WHERE 子句的一般语法 −[COMMAND] field,field2,... FROM table_name,table_name2,... WHERE [CONDITION]注意 WHERE 子句的以下特性 −它是可选的。它允许指定任意条件。它允许通过使用 AND 或 OR 操作符指定多个条件。大小写敏感性仅适用于使用 LIKE 比较的语句。WHERE 子句允许使用以下操作符 −操作符 ! WHERE 子句可以在命令提示符或 PHP 脚本中使用。命令提示符在命令提示符下只需使用标准命令 −roothost# 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 | ---------------------------------------------------查看使用AND条件的示例 −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);使用 WHERE 子句的 PHP 脚本在涉及 WHERE 子句的操作中使用mysql_query()函数 −?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); ?成功检索数据时您将看到以下输出 −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来源zjcp.cc