Yuav siv MySQL qhov twg nqe lus? qhov twg clause ntau conditional syntax

MySQL databaseYuav siv qhov twg nqe lus? qhov twg clause ntau yam xwm txheej syntax

MySQL THAUM clause

Peb paub siv SQL SELECT nqe lus los nyeem cov ntaub ntawv los ntawm MySQL cov lus.

Txhawm rau xaiv cov ntaub ntawv los ntawm lub rooj, ntxiv ib qho WHERE clause rau SELECT nqe lus.

qauv sau ntawv

Cov hauv qab no yog cov ntsiab lus dav dav ntawm SQL SELECT nqe lus los nyeem cov ntaub ntawv los ntawm cov ntaub ntawv cov ntaub ntawv siv WHERE clause:

SELECT field1, field2,...fieldN FROM table_name1, table_name2...
[WHERE condition1 [AND [OR]] condition2.....

• Koj tuaj yeem siv ib lossis ntau lub rooj nyob rau hauv nqe lus nug, siv commas ntawm cov ntxhuav, Sib cais, thiab siv cov lus hais nyob qhov twg los teeb tsa cov lus nug.
• Koj tuaj yeem hais qhia txhua yam xwm txheej hauv WHERE clause.
• Koj tuaj yeem teev ib lossis ntau yam kev siv uas siv THIAB lossis LOSSIS.
• Cov lus nyob qhov twg tuaj yeem siv nrog SQL's DELETE lossis UPDATE cov lus txib.
• Cov kab lus nyob qhov twg zoo ib yam li cov xwm txheej hauv cov lus txheej txheem, thiab nyeem cov ntaub ntawv teev tseg raws li tus nqi teb hauv MySQL cov lus.

Cov hauv qab no yog cov npe ntawm cov neeg ua haujlwm uas tuaj yeem siv tau hauv WHERE clause.

Cov piv txwv hauv cov lus hauv qab no xav tias A yog 10 thiab B yog 20

Qhov WHERE clause muaj txiaj ntsig zoo yog tias peb xav nyeem cov ntaub ntawv teev tseg los ntawm MySQL cov ntaub ntawv cov lus.

Kev siv tus yuam sij tseem ceeb raws li cov lus nug nyob hauv WHERE clause yog nrawm heev.

Yog tias cov txheej txheem muab tsis muaj cov ntaub ntawv sib txuam hauv lub rooj, cov lus nug rov qab tsis muaj ntaub ntawv.

nyeem cov ntaub ntawv los ntawm kev hais kom ua

Peb yuav siv WHERE clause hauv SQL SELECT nqe lus los nyeem cov ntaub ntawv hauv MySQL cov ntaub ntawv rooj chenweiliang_tbl:

piv txwv

Cov piv txwv hauv qab no yuav nyeem tag nrho cov ntaub ntawv hauv chenweiliang_tbl lub rooj uas tus nqi ntawm chenweiliang_author teb yog Sanjay:

Cov hlua sib piv hauv MySQL's WHERE clause yog qhov tsis txaus ntseeg.Koj tuaj yeem siv BINARY lo lus tseem ceeb los qhia tias kev sib piv txoj hlua nyob rau hauv qhov twg yog cov lus tseem ceeb.

Piv txwv li nram no:

mysql> SELECT * from chenweiliang_tbl WHERE BINARY chenweiliang_author='chenweiliang.com';
Empty set (0.01 sec)
 
mysql> SELECT * from chenweiliang_tbl WHERE BINARY chenweiliang_author='chenweiliang.com';
+-----------+---------------+---------------+-----------------+
| chenweiliang_id | chenweiliang_title | chenweiliang_author | submission_date |
+-----------+---------------+---------------+-----------------+
| 3 | JAVA 教程 | chenweiliang.com | 2016-05-06 |
| 4 | 学习 Python | chenweiliang.com | 2016-03-06 |
+-----------+---------------+---------------+-----------------+
2 rows in set (0.01 sec)

siv hauv qhov piv txwv PHOO lo lus tseem ceeb, yog case-sensitive, yog li ntawd chenweiliang_author = 'chenweiliang.com' Cov lus nug mob yog tsis muaj ntaub ntawv.

Nyeem cov ntaub ntawv siv PHP tsab ntawv

Koj tuaj yeem siv PHP ua haujlwm mysqli_query() thiab tib SQL SELECT cov lus txib nrog rau qhov twg los tau cov ntaub ntawv.

Cov haujlwm no yog siv los ua SQL cov lus txib thiab tom qab ntawd tso tawm tag nrho cov ntaub ntawv nug los ntawm PHP ua haujlwm mysqli_fetch_array().

piv txwv

Cov piv txwv hauv qab no yuav rov qab los ntawm chenweiliang_tbl lub rooj siv chenweiliang_author teb tus nqi raws li ntawm chenweiliang.com cov ntaub ntawv ntawm:

MySQL WHERE clause test:

<?
php
$dbhost = 'localhost:3306'; // mysql服务器主机地址
$dbuser = 'root'; // mysql用户名
$dbpass = '123456'; // mysql用户名密码
$conn = mysqli_connect($dbhost, $dbuser, $dbpass);
if(! $conn )
{
 die('连接失败: ' . mysqli_error($conn));
}
// 设置编码，防止中文乱码
mysqli_query($conn , "set names utf8");
 
// 读取 chenweiliang_author 为 chenweiliang.com 的数据
$sql = 'SELECT chenweiliang_id, chenweiliang_title, 
 chenweiliang_author, submission_date
 FROM chenweiliang_tbl
 WHERE chenweiliang_author="chenweiliang.com"';
 
mysqli_select_db( $conn, 'chenweiliang' );
$retval = mysqli_query( $conn, $sql );
if(! $retval )
{
 die('无法读取数据: ' . mysqli_error($conn));
}
echo '<h2>陈沩亮博客 MySQL WHERE 子句测试<h2>';
echo '<table border="1"><tr><td>教程 ID</td><td>标题</td><td>作者</td><td>提交日期</td></tr>';
while($row = mysqli_fetch_array($retval, MYSQL_ASSOC))
{
 echo "<tr><td> {$row['chenweiliang_id']}</td> ".
 "<td>{$row['chenweiliang_title']} </td> ".
 "<td>{$row['chenweiliang_author']} </td> ".
 "<td>{$row['submission_date']} </td> ".
 "</tr>";
}
echo '</table>';
// 释放内存
mysqli_free_result($retval);
mysqli_close($conn);
?>