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這篇文章主要為大家展示了“MySQL與PHP中的數(shù)據(jù)查詢語句是什么”,內(nèi)容簡而易懂,條理清晰,希望能夠幫助大家解決疑惑,下面讓小編帶領(lǐng)大家一起研究并學(xué)習(xí)一下“MySQL與PHP中的數(shù)據(jù)查詢語句是什么”這篇文章吧。
在 SQL 中, 我們可以使用 ORDER BY 對查詢結(jié)果進(jìn)行一列或多列排序.
SQL 語句:
SELECT 列名1, 列名2 FROM 表名1, 表名2
ORDER BY 列名, 列名[ASC|DESC]
注意:
ASC 表示按升序排列, DESC 表示按降序排列
默認(rèn)情況下對列按升序排序
表記錄:
工資從低到高排序:
<?php # 創(chuàng)建連接 $conn = mysqli_connect("localhost", "root", "admin", "study"); # 查看是否連接成功 if ($conn) { echo "服務(wù)器連接成功!\n"; } else { echo mysqli_connect_error(); } # SQL語句, 條件查詢 $SQL = "SELECT * FROM user ORDER BY salary"; # 執(zhí)行SQL語句 $result = mysqli_query($conn, $SQL); # 查看是否執(zhí)行成功 if ($result) { echo "SQL語句執(zhí)行成功!\n"; } else { echo mysqli_error($conn); } # 調(diào)試輸出 while ($line = mysqli_fetch_assoc($result)) { print_r($line); } # 關(guān)閉連接 mysqli_close($conn); ?>
輸出結(jié)果:
服務(wù)器連接成功!
SQL語句執(zhí)行成功!
Array
(
[id] => 3
[username] => 王富貴
[password] => 123456
[sex] => 1
[salary] => 1000.00
)
Array
(
[id] => 4
[username] => 李大爺
[password] => 123123
[sex] => 1
[salary] => 1500.00
)
Array
(
[id] => 2
[username] => 張美麗
[password] => 123456
[sex] => 2
[salary] => 5000.00
)
Array
(
[id] => 5
[username] => 王二狗
[password] => 123123
[sex] => 1
[salary] => 6000.00
)
Array
(
[id] => 1
[username] => 我是小白呀
[password] => 123456
[sex] => 2
[salary] => 30000.00
)
工資從高到低排序:
<?php # 創(chuàng)建連接 $conn = mysqli_connect("localhost", "root", "admin", "study"); # 查看是否連接成功 if ($conn) { echo "服務(wù)器連接成功!\n"; } else { echo mysqli_connect_error(); } # SQL語句, 條件查詢 $SQL = "SELECT * FROM user ORDER BY salary DESC"; # 執(zhí)行SQL語句 $result = mysqli_query($conn, $SQL); # 查看是否執(zhí)行成功 if ($result) { echo "SQL語句執(zhí)行成功!\n"; } else { echo mysqli_error($conn); } # 調(diào)試輸出 while ($line = mysqli_fetch_assoc($result)) { print_r($line); } # 關(guān)閉連接 mysqli_close($conn); ?>
我們可以在 SELECT 語句中使用 LIMIT 來約束要返回的記錄數(shù), 通常使用 LIMIT 實(shí)現(xiàn)分頁.
SQL 語句:
SELECT 列名1, 列名2 FROM 表1, 表2 LIMIT [偏移量] 行數(shù)
注意:
第一行的偏移量是 0, 而不是 1
行數(shù)為返回最大的行數(shù)
取前兩個(gè)數(shù)據(jù):
<?php # 創(chuàng)建連接 $conn = mysqli_connect("localhost", "root", "admin", "study"); # 查看是否連接成功 if ($conn) { echo "服務(wù)器連接成功!\n"; } else { echo mysqli_connect_error(); } # SQL語句 $SQL = "SELECT * FROM user LIMIT 2"; # 執(zhí)行SQL語句 $result = mysqli_query($conn, $SQL); # 查看是否執(zhí)行成功 if ($result) { echo "SQL語句執(zhí)行成功!\n"; } else { echo mysqli_error($conn); } # 調(diào)試輸出 while ($line = mysqli_fetch_assoc($result)) { print_r($line); } # 關(guān)閉連接 mysqli_close($conn); ?>
輸出結(jié)果:
服務(wù)器連接成功!
SQL語句執(zhí)行成功!
Array
(
[id] => 1
[username] => 我是小白呀
[password] => 123456
[sex] => 2
[salary] => 30000.00
)
Array
(
[id] => 2
[username] => 張美麗
[password] => 123456
[sex] => 2
[salary] => 5000.00
)
取第 2, 3 條數(shù)據(jù):
<?php # 創(chuàng)建連接 $conn = mysqli_connect("localhost", "root", "admin", "study"); # 查看是否連接成功 if ($conn) { echo "服務(wù)器連接成功!\n"; } else { echo mysqli_connect_error(); } # SQL語句 $SQL = "SELECT * FROM user LIMIT 1, 2"; # 執(zhí)行SQL語句 $result = mysqli_query($conn, $SQL); # 查看是否執(zhí)行成功 if ($result) { echo "SQL語句執(zhí)行成功!\n"; } else { echo mysqli_error($conn); } # 調(diào)試輸出 while ($line = mysqli_fetch_assoc($result)) { print_r($line); } # 關(guān)閉連接 mysqli_close($conn); ?>
輸出結(jié)果:
服務(wù)器連接成功!
SQL語句執(zhí)行成功!
Array
(
[id] => 2
[username] => 張美麗
[password] => 123456
[sex] => 2
[salary] => 5000.00
)
Array
(
[id] => 3
[username] => 王富貴
[password] => 123456
[sex] => 1
[salary] => 1000.00
)
從字面上理解, GROUP BY 表示根據(jù)某種規(guī)則對數(shù)據(jù)進(jìn)行分組. 它必須配合聚合函數(shù)進(jìn)行使用, 對數(shù)據(jù)進(jìn)行分組后可以進(jìn)行 COUNT, SUM, AVG, MAX 和 MIN 等運(yùn)算.
SQL 語句:
SELECT 列名, 聚合函數(shù)(列名)
FROM 表名
GROUP BY 列名
注意:
GROUP BY 可以對一列或多列進(jìn)行分組
表記錄:
<?php # 創(chuàng)建連接 $conn = mysqli_connect("localhost", "root", "admin", "study"); # 查看是否連接成功 if ($conn) { echo "服務(wù)器連接成功!\n"; } else { echo mysqli_connect_error(); } # SQL語句 $SQL = "SELECT gender, count(*) FROM student GROUP BY gender"; # 執(zhí)行SQL語句 $result = mysqli_query($conn, $SQL); # 查看是否執(zhí)行成功 if ($result) { echo "SQL語句執(zhí)行成功!\n"; } else { echo mysqli_error($conn); } # 調(diào)試輸出 while ($line = mysqli_fetch_assoc($result)) { print_r($line); } # 關(guān)閉連接 mysqli_close($conn); ?>
輸出結(jié)果:
服務(wù)器連接成功!
SQL語句執(zhí)行成功!
Array
(
[gender] => 1
[count(*)] => 3
)
Array
(
[gender] => 2
[count(*)] => 6
)
<?php # 創(chuàng)建連接 $conn = mysqli_connect("localhost", "root", "admin", "study"); # 查看是否連接成功 if ($conn) { echo "服務(wù)器連接成功!\n"; } else { echo mysqli_connect_error(); } # SQL語句 $SQL = "SELECT grade, count(*) FROM student GROUP BY grade"; # 執(zhí)行SQL語句 $result = mysqli_query($conn, $SQL); # 查看是否執(zhí)行成功 if ($result) { echo "SQL語句執(zhí)行成功!\n"; } else { echo mysqli_error($conn); } # 調(diào)試輸出 while ($line = mysqli_fetch_assoc($result)) { print_r($line); } # 關(guān)閉連接 mysqli_close($conn); ?>
輸出結(jié)果:
服務(wù)器連接成功!
SQL語句執(zhí)行成功!
Array
(
[grade] => 高三
[count(*)] => 2
)
Array
(
[grade] => 高一
[count(*)] => 4
)
Array
(
[grade] => 高二
[count(*)] => 3
)
HAVING 可以解決 WHERE 關(guān)鍵詞無法與聚合函數(shù)一起使用的問題. HAVING 可以對分組后的各組數(shù)據(jù)進(jìn)行篩選.
SQL 語句:
SELECT 列名, 聚合函數(shù)(列名)
FROM 表名
GROUP BY 列名
HAVING 聚合函數(shù)(列名) 條件
<?php # 創(chuàng)建連接 $conn = mysqli_connect("localhost", "root", "admin", "study"); # 查看是否連接成功 if ($conn) { echo "服務(wù)器連接成功!\n"; } else { echo mysqli_connect_error(); } # SQL語句 $SQL = "SELECT grade, count(*) FROM student GROUP BY grade HAVING count(*) > 2"; # 執(zhí)行SQL語句 $result = mysqli_query($conn, $SQL); # 查看是否執(zhí)行成功 if ($result) { echo "SQL語句執(zhí)行成功!\n"; } else { echo mysqli_error($conn); } # 調(diào)試輸出 while ($line = mysqli_fetch_assoc($result)) { print_r($line); } # 關(guān)閉連接 mysqli_close($conn); ?>
輸出結(jié)果:
服務(wù)器連接成功!
SQL語句執(zhí)行成功!
Array
(
[grade] => 高一
[count(*)] => 4
)
Array
(
[grade] => 高二
[count(*)] => 3
)
<?php # 創(chuàng)建連接 $conn = mysqli_connect("localhost", "root", "admin", "study"); # 查看是否連接成功 if ($conn) { echo "服務(wù)器連接成功!\n"; } else { echo mysqli_connect_error(); } # SQL語句 $SQL = "SELECT gender, count(*) FROM student GROUP BY gender HAVING count(*) > 3"; # 執(zhí)行SQL語句 $result = mysqli_query($conn, $SQL); # 查看是否執(zhí)行成功 if ($result) { echo "SQL語句執(zhí)行成功!\n"; } else { echo mysqli_error($conn); } # 調(diào)試輸出 while ($line = mysqli_fetch_assoc($result)) { print_r($line); } # 關(guān)閉連接 mysqli_close($conn); ?>
輸出結(jié)果:
服務(wù)器連接成功!
SQL語句執(zhí)行成功!
Array
(
[gender] => 2
[count(*)] => 6
)
當(dāng)我們使用GROUP BY
可以獲取分組, 但是無法看到具體信息. 這時(shí)我們就可以使用GROUP_CONCAT
來獲取具體信息. GROUP_CONCAT
配合GROUP BY
一起使用, 可以將一列的值按照指定分隔符進(jìn)行拼接 (默認(rèn)為 “,”).
SQL 語句:
GROUP_CONCAT(列名[排序列 ASC/DESC] [分隔符])
<?php $conn = mysqli_connect("localhost", "root","admin","study"); if ($conn) { echo "數(shù)據(jù)庫鏈接成功"; } else { echo mysqli_connect_error(); } # SQL語句 $SQL = "SELECT grade, count(*), GROUP_CONCAT(student_name) FROM student GROUP BY grade"; # 執(zhí)行 $result = mysqli_query($conn, $SQL); # 查看是否執(zhí)行成功 if ($result) { echo "SQL 語句執(zhí)行成功!"; }else { echo mysqli_error($conn); } # 調(diào)試輸出 while ($line = mysqli_fetch_assoc($result)) { print_r($line); } # 關(guān)閉連接 mysqli_close($conn); ?>
輸出結(jié)果:
數(shù)據(jù)庫鏈接成功SQL 語句執(zhí)行成功!Array
(
[grade] => 高一
[count(*)] => 4
[GROUP_CONCAT(student_name)] => 王富貴,楊美麗,楊美麗,楊美麗
)
Array
(
[grade] => 高三
[count(*)] => 2
[GROUP_CONCAT(student_name)] => 楊美麗,楊美麗
)
Array
(
[grade] => 高二
[count(*)] => 3
[GROUP_CONCAT(student_name)] => 楊美麗,楊美麗,趙有才
)
<?php $conn = mysqli_connect("localhost", "root","admin","study"); if ($conn) { echo "數(shù)據(jù)庫鏈接成功"; } else { echo mysqli_connect_error(); } # SQL語句 $SQL = "SELECT gender, count(*), GROUP_CONCAT(student_name) FROM student GROUP BY gender"; # 執(zhí)行 $result = mysqli_query($conn, $SQL); # 查看是否執(zhí)行成功 if ($result) { echo "SQL 語句執(zhí)行成功!"; }else { echo mysqli_error($conn); } # 調(diào)試輸出 while ($line = mysqli_fetch_assoc($result)) { print_r($line); } # 關(guān)閉連接 mysqli_close($conn); ?>
輸出結(jié)果:
數(shù)據(jù)庫鏈接成功SQL 語句執(zhí)行成功!Array
(
[gender] => 1
[count(*)] => 3
[GROUP_CONCAT(student_name)] => 楊美麗,楊美麗,楊美麗
)
Array
(
[gender] => 2
[count(*)] => 6
[GROUP_CONCAT(student_name)] => 王富貴,楊美麗,楊美麗,楊美麗,楊美麗,趙有才
)
DISTINCT
用于在查詢中返回父唯一不同值, 支持單列或多列. 在實(shí)際的應(yīng)用中, 表中的某一列含有重復(fù)值是很常見的. 如果在查詢數(shù)據(jù)時(shí), 希望得到某列的所有不同值, 可以使用 DISTINCT
.
SQL 語句:
SELECT DISTINCT 列名1, 列名2 FROM 表名
<?php $conn = mysqli_connect("localhost", "root","admin","study"); if ($conn) { echo "數(shù)據(jù)庫鏈接成功"; } else { echo mysqli_connect_error(); } # SQL語句 $SQL = "SELECT DISTINCT grade FROM student"; # 執(zhí)行 $result = mysqli_query($conn, $SQL); # 查看是否執(zhí)行成功 if ($result) { echo "SQL 語句執(zhí)行成功!"; }else { echo mysqli_error($conn); } # 調(diào)試輸出 while ($line = mysqli_fetch_assoc($result)) { print_r($line); } # 關(guān)閉連接 mysqli_close($conn); ?>
輸出結(jié)果:
數(shù)據(jù)庫鏈接成功SQL 語句執(zhí)行成功!Array
(
[grade] => 高三
)
Array
(
[grade] => 高一
)
Array
(
[grade] => 高二
)
<?php $conn = mysqli_connect("localhost", "root","admin","study"); if ($conn) { echo "數(shù)據(jù)庫鏈接成功"; } else { echo mysqli_connect_error(); } # SQL語句 $SQL = "SELECT DISTINCT gender FROM student"; # 執(zhí)行 $result = mysqli_query($conn, $SQL); # 查看是否執(zhí)行成功 if ($result) { echo "SQL 語句執(zhí)行成功!"; }else { echo mysqli_error($conn); } # 調(diào)試輸出 while ($line = mysqli_fetch_assoc($result)) { print_r($line); } # 關(guān)閉連接 mysqli_close($conn); ?>
輸出結(jié)果:
數(shù)據(jù)庫鏈接成功SQL 語句執(zhí)行成功!Array
(
[gender] => 1
)
Array
(
[gender] => 2
)
以上是“MySQL與PHP中的數(shù)據(jù)查詢語句是什么”這篇文章的所有內(nèi)容,感謝各位的閱讀!相信大家都有了一定的了解,希望分享的內(nèi)容對大家有所幫助,如果還想學(xué)習(xí)更多知識(shí),歡迎關(guān)注億速云行業(yè)資訊頻道!
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