我有以下表格:
table_categories - id, name, imagepath
table_subcategories - sub_categories_id, sub_category_name
table_subcategory_categories - subcategory_id, category_id (Mapping table for category and sub category)
我想以这种格式获取所有类别及其各自的子类别:
[
{
"subcategories": [
{
"scname": "Sugar",
"scid": "5"
},
{
"scname": "Salt",
"scid": "6"
},
{
"scname": "Jaggery",
"scid": "7"
}
],
"name": "Salt and Sugar",
"id": "1",
"image": "/images/salt_sugar.png"
},
{
"subcategories": [
{
"scname": "Tea",
"scid": "8"
},
{
"scname": "Coffee",
"scid": "9"
},
{
"scname": "Tea Bags",
"scid": "162"
}
],
"name": "Tea and Coffee",
"id": "2",
"image": "/images/tea_and_coffee.png"
}
]
这是我获取类别和子类别的逻辑。
my $sql_query = "SELECT * from table_categories";
my $statement = $db_handle->prepare ($sql_query) or die "Couldn't prepare query '$sql_query': $DBI::errstr\n";
$statement->execute() or die "SQL Error: $DBI::errstr\n";
my @loop_data = ();
while (my @data = $statement->fetchrow_array()) {
my $sql = "SELECT SCC.subcategory_id, SC.sub_category_name
FROM
table_subcategory_categories as SCC
INNER JOIN
table_subcategories as SC
ON
SCC.subcategory_id = SC.sub_categories_id
where SCC.category_id = '$data[0]' ";
my $stmt = $db_handle->prepare ($sql) or die "Couldn't prepare query '$sql_query': $DBI::errstr\n";
$stmt->execute() or die "SQL Error: $DBI::errstr\n";
my @InnerLoopData = ();
while (my @InnerData = $stmt->fetchrow_array()) {
my %InnerData = ('scid', $InnerData[0], 'scname', $InnerData[1]);
push(@InnerLoopData, \%InnerData);
}
my %data = ('id', $data[0], 'name', $data[1], 'image', $data[2], 'subcategories', \@InnerLoopData);
push(@loop_data, \%data);
}
my $json_text = to_json(\@loop_data);
print $json_text;
$db_handle->disconnect;
一切正常,但问题是由于内部查询响应太慢。由于我有1000多个类别,内部查询执行了1000多次。
能否请任何人帮助我如何优化此查询?
最佳答案
您可以在perl脚本中进行处理,以减少数据库调用的次数。数据库调用很昂贵。
以排序的方式获取表类别的列表。
SELECT * FROM table_categories ORDER BY id ASC
将值存储在多维数组中。说出类别
获取数组中每个类别的计数。再次排序。保存在数组中,例如category_count
按category_id从table_subcategory_categories组中选择count(*),按category_id ASC选择顺序
获取按类别排序的整个子类别列表
保存在多维数组中,请说sub_categories
从table_subcategories sc,table_subcategory_categories scc WHERE sc.sub_categories_id = scc.sub_categories_id中选择sc。*,scc.category_id排序依据scc.category_id ASC
接着
my @loop_data = ();
my $currentPos = 0;
my $noOfElementsInThisCategory = 0;
foreach my $i (0 .. $#categories){
$noOfElementsInThisCategory = $category_count[$i];
my @InnerLoopData = ();
for (my $k = $currentPos; $noOfElementsInThisCategory > 0; $noOfElementsInThisCategory++) {
my %InnerData = ('scid', $sub_categories [$k][0], 'scname', $sub_categories [$k][1]);
push(@InnerLoopData, \%InnerData);
$currentPos = $currentPos + 1;
}
my %data = ('id', $categories[$i][0], 'name', $categories[$i][1], 'image', $categories[$i][2], 'subcategories', \@InnerLoopData);
push(@loop_data, \%data);
}
my $json_text = to_json(\@loop_data);
print $json_text;