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* Add docs for HAVING + GROUP BY clause Signed-off-by: Shivam Sandbhor <shivam.sandbhor@gmail.com> * Make review changes for docs Signed-off-by: Shivam Sandbhor <shivam.sandbhor@gmail.com>
140 lines
2.4 KiB
Markdown
Executable File
140 lines
2.4 KiB
Markdown
Executable File
---
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id: aggregate
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title: Aggregation
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---
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## Group By
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Group by `name` and `age` fields of all users, and sum their total age.
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```go
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package main
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import (
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"context"
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"<project>/ent"
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"<project>/ent/user"
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)
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func Do(ctx context.Context, client *ent.Client) {
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var v []struct {
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Name string `json:"name"`
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Age int `json:"age"`
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Sum int `json:"sum"`
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Count int `json:"count"`
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}
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err := client.User.Query().
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GroupBy(user.FieldName, user.FieldAge).
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Aggregate(ent.Count(), ent.Sum(user.FieldAge)).
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Scan(ctx, &v)
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}
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```
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Group by one field.
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```go
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package main
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import (
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"context"
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"<project>/ent"
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"<project>/ent/user"
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)
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func Do(ctx context.Context, client *ent.Client) {
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names, err := client.User.
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Query().
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GroupBy(user.FieldName).
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Strings(ctx)
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}
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```
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## Group By Edge
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Custom aggregation functions can be useful if you want to write your own storage-specific logic.
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The following shows how to group by the `id` and the `name` of all users and calculate the average `age` of their pets.
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```go
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package main
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import (
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"context"
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"log"
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"<project>/ent"
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"<project>/ent/pet"
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"<project>/ent/user"
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)
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func Do(ctx context.Context, client *ent.Client) {
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var users []struct {
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ID int
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Name string
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Average float64
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}
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err := client.User.Query().
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GroupBy(user.FieldID, user.FieldName).
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Aggregate(func(s *sql.Selector) string {
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t := sql.Table(pet.Table)
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s.Join(t).On(s.C(user.FieldID), t.C(pet.OwnerColumn))
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return sql.As(sql.Avg(t.C(pet.FieldAge)), "average")
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}).
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Scan(ctx, &users)
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}
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```
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## Having + Group By
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This example requires custom SQL modifiers. See how to enable them [here](https://entgo.io/docs/feature-flags/#custom-sql-modifiers)
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In this example we're going to query the oldest users for each role.
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```go
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package main
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import (
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"context"
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"log"
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"entgo.io/ent/dialect/sql"
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"<project>/ent"
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"<project>/ent/user"
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)
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func Do(ctx context.Context, client *ent.Client) {
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var users []struct {
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Id Int
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Age Int
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Role string
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}
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client.User.Query().Modify(
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func(s *sql.Selector) {
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s.GroupBy(
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User.Role,
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)
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s.Having(
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sql.EQ(
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user.FieldAge,
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sql.Raw(sql.Max(user.FieldAge)),
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),
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)
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}
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).ScanX(ctx, &users)
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}
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```
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**Note:** The `sql.Raw` is crucial to have. It tells the predicate that `sql.Max` is not an arguement.
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The above code essentially generates the following SQL query:
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```sql
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SELECT * FROM user
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GROUP BY user.role
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HAVING user.age = MAX(user.age) ;
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``` |