MySQL是一個(gè)關(guān)系型數(shù)據(jù)庫管理系統(tǒng)，由瑞典MySQL?AB?公司開發(fā)，屬于?Oracle?旗下產(chǎn)品。MySQL?是最流行的關(guān)系型數(shù)據(jù)庫管理系統(tǒng)之一，本系列將帶你掌握php與mysql的基礎(chǔ)應(yīng)用，本篇表連接開始

概述

從今天開始, 小白我將帶領(lǐng)大家一起來補(bǔ)充一下數(shù)據(jù)庫的知識.

表連接

表連接 (JOIN) 是在多個(gè)表之間通過連接條件. 使表之間發(fā)生關(guān)聯(lián), 進(jìn)而能從多個(gè)表之間獲取數(shù)據(jù).

表連接語法:

SELECT 表名1.列名, 表名2.列名 FROM 表1, 表2 WHERE 條件

表連接的幾種方式:

內(nèi)連接: join 或者 inner join

自連接: 同一張表內(nèi)的連接

外連接:

左外連接, left join
右外連接, right join
全外連接, full join

數(shù)據(jù) (table1):

數(shù)據(jù) (table2):

內(nèi)連接

內(nèi)連接是從結(jié)果表中刪除與其他被連接表中沒有匹配的所有行. (交集)

格式:

SELECT A.c1, B.c2 FROM A JOIN B ON A.c3 = B.c3

例子:

<?php

$conn = mysqli_connect("localhost", "root","admin","study");

if ($conn) {
    echo "數(shù)據(jù)庫鏈接成功\n";
} else {
    echo mysqli_connect_error();
}

# SQL語句
$SQL = "SELECT table1.name, table1.age, table2.class
        FROM table1 JOIN table2
        ON table1.name = table2.name";

# 執(zhí)行
$result = mysqli_query($conn, $SQL);

# 查看是否執(zhí)行成功
if ($result) {
    echo "SQL 語句執(zhí)行成功!\n";
}else {
    echo mysqli_error($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:

數(shù)據(jù)庫鏈接成功
SQL 語句執(zhí)行成功!
Array
(
[name] => 楊富貴
[age] => 18
[class] => 數(shù)學(xué)課
)
Array
(
[name] => 楊美麗
[age] => 19
[class] => 語文課
)
Array
(
[name] => 楊建國
[age] => 20
[class] => 英語課
)

左連接

包含做表的全部行 (不管右表是否存在與之匹配的行), 以及右表中全部匹配的行.

格式:

SELECT A.c1, B.c2 FROM A LEFT JOIN B ON A.c3 = B.c3

例子:

<?php

$conn = mysqli_connect("localhost", "root","admin","study");

if ($conn) {
    echo "數(shù)據(jù)庫鏈接成功\n";
} else {
    echo mysqli_connect_error();
}

# SQL語句
$SQL = "SELECT table1.name, table1.age, table2.class
        FROM table1 LEFT JOIN table2
        ON table1.name = table2.name";

# 執(zhí)行
$result = mysqli_query($conn, $SQL);

# 查看是否執(zhí)行成功
if ($result) {
    echo "SQL 語句執(zhí)行成功!\n";
}else {
    echo mysqli_error($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:

數(shù)據(jù)庫鏈接成功
SQL 語句執(zhí)行成功!
Array
(
[name] => 楊富貴
[age] => 18
[class] => 數(shù)學(xué)課
)
Array
(
[name] => 楊美麗
[age] => 19
[class] => 語文課
)
Array
(
[name] => 楊建國
[age] => 20
[class] => 英語課
)
Array
(
[name] => 楊鐵柱
[age] => 21
[class] =>
)

右連接

包含右表的全部行 (不管左表是否存在與之匹配的行), 以及左表中全部匹配的行.

格式:

SELECT A.c1, B.c2 FROM A RIGHT JOIN B ON A.c3 = B.c3

例子:

<?php

$conn = mysqli_connect("localhost", "root","admin","study");

if ($conn) {
    echo "數(shù)據(jù)庫鏈接成功\n";
} else {
    echo mysqli_connect_error();
}

# SQL語句
$SQL = "SELECT table1.name, table1.age, table2.class
        FROM table1 RIGHT JOIN table2
        ON table1.name = table2.name";

# 執(zhí)行
$result = mysqli_query($conn, $SQL);

# 查看是否執(zhí)行成功
if ($result) {
    echo "SQL 語句執(zhí)行成功!\n";
}else {
    echo mysqli_error($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:

數(shù)據(jù)庫鏈接成功
SQL 語句執(zhí)行成功!
Array
(
[name] => 楊富貴
[age] => 18
[class] => 數(shù)學(xué)課
)
Array
(
[name] => 楊美麗
[age] => 19
[class] => 語文課
)
Array
(
[name] => 楊建國
[age] => 20
[class] => 英語課
)
Array
(
[name] =>
[age] =>
[class] => 歷史課
)

全連接

包含左右兩個(gè)表的全部行 (不管在另一個(gè)表中是否存在與之匹配的行).

格式:

SELECT A.c1, B.c2 FROM A LEFT JOIN B ON A.c3 = B.c3
UNION
SELECT A.c1, B.c2 FROM A RIGHT JOIN B ON A.c3 = B.c3

例子:

<?php

$conn = mysqli_connect("localhost", "root","admin","study");

if ($conn) {
    echo "數(shù)據(jù)庫鏈接成功\n";
} else {
    echo mysqli_connect_error();
}

# SQL語句
$SQL = "SELECT table1.name, table1.age, table2.class
        FROM table1 LEFT JOIN table2 ON table1.name = table2.name
        UNION 
        SELECT table1.name, table1.age, table2.class
        FROM table1 RIGHT JOIN table2 ON table1.name = table2.name";

# 執(zhí)行
$result = mysqli_query($conn, $SQL);

# 查看是否執(zhí)行成功
if ($result) {
    echo "SQL 語句執(zhí)行成功!\n";
}else {
    echo mysqli_error($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:

數(shù)據(jù)庫鏈接成功
SQL 語句執(zhí)行成功!
Array
(
[name] => 楊富貴
[age] => 18
[class] => 數(shù)學(xué)課
)
Array
(
[name] => 楊美麗
[age] => 19
[class] => 語文課
)
Array
(
[name] => 楊建國
[age] => 20
[class] => 英語課
)
Array
(
[name] => 楊鐵柱
[age] => 21
[class] =>
)
Array
(
[name] =>
[age] =>
[class] => 歷史課
)