How to insert with select using GORM? - mysql

Question

Is there a way to insert(create) rows with select in a single query using GORM?
What I am trying to do is to join two tables and insert rows into another table using a selected value from the table (using insert/select) but I'm having a hard time finding a way to call create along with select using GORM.
Basically what I hope to do can be done in a below SQL query:
INSERT INTO table_two (val, name, age)
SELECT table_one.some_value, '', 0
FROM table_one
WHERE table_one.some_value = 50
This inserts new rows into table_two with val column values set to the some_value of each of the matched rows in table_one.
Thanks in advance.

Answer 1

I was able to implement your request in two ways.
The first approach is to use a raw SQL Query (the same that you provide in your question). Thanks to the db.Exec() function you're able to run a raw SQL statement against your MySQL instance.
The second approach is to split the operation into two parts:
First you read the data with Where and Find
Second you insert the data with Create
Below, you can find both solutions:
package main
import (
"gorm.io/driver/mysql"
"gorm.io/gorm"
)
type TableOne struct {
SomeValue int
Name string
Age int
}
type TableTwo struct {
Val int
Name string
Age int
}
func main() {
// refer https://github.com/go-sql-driver/mysql#dsn-data-source-name for details
dsn := "root:root#tcp(127.0.0.1:3306)/todo?charset=utf8mb4&parseTime=True&loc=Local"
db, err := gorm.Open(mysql.Open(dsn), &gorm.Config{})
if err != nil {
panic(err)
}
// first approach - Raw SQL
if dbTrn := db.Exec(`INSERT INTO table_twos (val, name, age)
SELECT table_ones.some_value, '', 0
FROM table_ones
WHERE table_ones.some_value = 50`).Error; dbTrn != nil {
panic(dbTrn.Error)
}
// second approach - split into two actions
var recordsOne []TableOne
recordsTwo := make([]TableTwo, 0)
db.Where("some_value=?", 50).Find(&recordsOne)
for _, v := range recordsOne {
recordsTwo = append(recordsTwo, TableTwo{Val: v.SomeValue, Name: "", Age: 0})
}
db.Create(&recordsTwo)
}
Let me know if this works also for you.