Group Aggregation Query

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static IFreeSql fsql = new FreeSql.FreeSqlBuilder()
    .UseConnectionString(FreeSql.DataType.MySql, connectionString)
     //Be sure to define as singleton mode
    .Build(); 

class Topic 
{
    [Column(IsIdentity = true, IsPrimary = true)]
    public int Id { get; set; }
    public int Clicks { get; set; }
    public string Title { get; set; }
    public DateTime CreateTime { get; set; }
}

Group Aggregation

var list = fsql.Select<Topic>()
    .GroupBy(a => new { tt2 = a.Title.Substring(0, 2), mod4 = a.Id % 4 })
    .Having(a => a.Count() > 0 && a.Avg(a.Key.mod4) > 0 && a.Max(a.Key.mod4) > 0)
    .Having(a => a.Count() < 300 || a.Avg(a.Key.mod4) < 100)
    .OrderBy(a => a.Key.tt2)
    .OrderByDescending(a => a.Count())
    .ToList(a => new 
    {
        a.Key, 
        cou1 = a.Count(), 
        arg1 = a.Avg(a.Value.Clicks), 
        arg2 = a.Sum(a.Value.Clicks > 100 ? 1 : 0)
    });

//SELECT 
//substr(a.`Title`, 1, 2) as1, 
//count(1) as2, 
//avg(a.`Clicks`) as3, 
//sum(case when a.`Clicks` > 100 then 1 else 0 end) as4 
//FROM `Topic` a 
//GROUP BY substr(a.`Title`, 1, 2), (a.`Id` % 4) 
//HAVING (count(1) > 0 AND avg((a.`Id` % 4)) > 0 AND max((a.`Id` % 4)) > 0) AND (count(1) < 300 OR avg((a.`Id` % 4)) < 100)
//ORDER BY substr(a.`Title`, 1, 2), count(1) DESC

To find the aggregate value without grouping, please use ToAggregate instead of ToList

var list = fsql.Select<Topic>()
    .ToAggregate(a => new 
    {
        cou1 = a.Count(), 
        arg1 = a.Avg(a.Key.Clicks), 
        arg2 = a.Sum(a.Key.Clicks > 100 ? 1 : 0)
    });

Navigation Property Grouping

If Topic has the navigation property Category, and Category has the navigation property Area, the navigation property grouping code is as follows:

var list = fsql.Select<Topic>()
    .GroupBy(a => new { a.Clicks, a.Category })
    .ToList(a => new { a.Key.Category.Area.Name });

Note: Write as above, an error will be reported and cannot be resolved a.Key.Category.Area.Name. The solution is to use Include:

var list = fsql.Select<Topic>()
    .Include(a => a.Category.Area)
    //This line must be added, 
    //otherwise only the Category will be grouped without its sub-navigation property Area

    .GroupBy(a => new { a.Clicks, a.Category })
    .ToList(a => new { a.Key.Category.Area.Name });

However, you can also solve it like this:

var list = fsql.Select<Topic>()
    .GroupBy(a => new { a.Clicks, a.Category, a.Category.Area })
    .ToList(a => new { a.Key.Area.Name });

Multi-table Grouping

var list = fsql.Select<Topic, Category, Area>()
    .GroupBy((a, b, c) => new { a.Title, c.Name })
    .Having(g => g.Count() < 300 || g.Avg(g.Value.Item1.Clicks) < 100)
    .ToList(g => new { count = g.Count(), Name = g.Key.Name });

• g.Value.Item1 corresponds to Topic
• g.Value.Item2 corresponds to Category
• g.Value.Item3 corresponds to Area

说明	方法	SQL
总数	.Count()	select count(*) from ...
求和	.Sum(a => a.Score)	select sum([Score]) from ...
平均	.Avg(a => a.Score)	select avg([Score]) from ...
最大值	.Max(a => a.Score)	select max([Score]) from ...
最小值	.Min(a => a.Score)	select min([Score]) from ...

lambda	sql	说明
SqlExt.IsNull(id, 0)	isnull/ifnull/coalesce/nvl	兼容各大数据库
SqlExt.DistinctCount(id)	count(distinct id)
SqlExt.GreaterThan	>	大于
SqlExt.GreaterThanOrEqual	>=	大于或等于
SqlExt.LessThan	<	小于
SqlExt.LessThanOrEqual	<=	小于
SqlExt.EqualIsNull	IS NULL	是否为 NULL
SqlExt.Case(字典)	case when .. end	根据字典 case
SqlExt.GroupConcat	group_concat(distinct .. order by .. separator ..)	MySql
SqlExt.FindInSet	find_in_set(str, strlist)	MySql
SqlExt.StringAgg	string_agg(.., ..)	PostgreSQL
SqlExt.Rank().Over().PartitionBy().ToValue()	rank() over(partition by xx)	开窗函数
SqlExt.DenseRank().Over().PartitionBy().ToValue()	dense_rank() over(partition by xx)
SqlExt.Count(id).Over().PartitionBy().ToValue()	count(id) over(partition by xx)
SqlExt.Sum(id).Over().PartitionBy().ToValue()	sum(id) over(partition by xx)
SqlExt.Avg(id).Over().PartitionBy().ToValue()	avg(id) over(partition by xx)
SqlExt.Max(id).Over().PartitionBy().ToValue()	max(id) over(partition by xx)
SqlExt.Min(id).Over().PartitionBy().ToValue()	min(id) over(partition by xx)
SqlExt.RowNumber(id).Over().PartitionBy().ToValue()	row_number(id) over(partition by xx)

Query first record on GroupBy

fsql.Select<User1>()
    .Where(a => a.Id < 1000)
    .WithTempQuery(a => new
    {
        item = a,
        rownum = SqlExt.RowNumber().Over().PartitionBy(a.Nickname).OrderBy(a.Id).ToValue()
    })
    .Where(a => a.rownum == 1)
    .ToList();

SELECT *
FROM (
    SELECT a.[Id], a.[Nickname], row_number() over( partition by a.[Nickname] order by a.[Id]) [rownum]
    FROM [User1] a
    WHERE a.[Id] < 1000
) a
WHERE (a.[rownum] = 1)

or：

fsql.Select<User1>()
    .Where(a => a.Id < 1000)
    .GroupBy(a => a.Nickname)
    .WithTempQuery(g => new { min = g.Min(g.Value.Id) })
    .From<User1>()
    .InnerJoin((a, b) => a.min == b.Id)
    .ToList((a, b) => b);

SELECT b.[Id], b.[Nickname] 
FROM ( 
    SELECT min(a.[Id]) [min] 
    FROM [User1] a 
    WHERE a.[Id] < 1000 
    GROUP BY a.[Nickname] ) a 
INNER JOIN [User1] b ON a.[min] = b.[Id]

more.. 《Nested Query》

Aggregate

• Distinct

var list = fsql.Select<Topic>()
    .Aggregate(a => Convert.ToInt32("count(distinct title)"), out var count)
    .ToList();

• SqlExt.DistinctCount

fsql.Select<Topic>()
    .Aggregate(a => SqlExt.DistinctCount(a.Key.Title), out var count);

SELECT count(distinct a."title") as1 FROM "Topic" a

API

Method	Return	Parameter	Description
ToSql	string		Return the SQL statement to be executed
ToList<T>	List<T>	Lambda	Execute SQL query and return the records of the specified field. When the record does not exist, return a list with Count of 0.
ToList<T>	List<T>	string field	Execute SQL query, and return the record of the field specified by field, and receive it as a tuple or basic type (int, string, long). If the record does not exist, return a list with Count of 0.
ToAggregate<T>	List<T>	Lambda	Execute SQL query and return the aggregate result of the specified field. (Suitable for scenarios where GroupBy is not required)
Sum	T	Lambda	Specify a column to sum.
Min	T	Lambda	Specify a column to find the minimum.
Max	T	Lambda	Specify a column to find the maximum.
Avg	T	Lambda	Specify a column to average.
【Grouping】
GroupBy	<this>	Lambda	Group by the selected column, GroupBy(a => a.Name)
GroupBy	<this>	string, parms	Group by raw sql statement, GroupBy("concat(name, @cc)", new { cc = 1 })
Having	<this>	string, parms	Filter by raw SQL statement aggregation conditions, Having("count(name) = @cc", new { cc = 1 })
【Members】
Key			Returns the object selected by GroupBy
Value			Return to the main table or the field selector of From<T2,T3....>

Reference

• 《Query from Multi Tables》
• 《Return Data》
• 《LinqToSql》
• 《Repository Layer》
• 《Filters and Global Filters》
• 《FreeSql Optimization: Lazy Loading》
• 《FreeSql Optimization: Greed Loading》
• 《Expression Function》
• 《Performance》
• 《Tenant》