Gorm Use *DB.Row(sql string, values ...interface{}) method directly occur Error 1040: Too many connections

gorm v1.25.1

dsn := "root:xxx@tcp(127.0.0.1:3306)/xxx?charset=utf8mb4&parseTime=True&loc=Local"
gormDb, err := gorm.Open(gormMySQL.Open(dsn))
writeConn := gormDb.WriteDB
_, err := writeConn.Raw("sql clause").Rows

when I execute writeConn.Raw("sql clause").Rows multiple times, then I will occur Error 1040: Too many connections , but If I change to below, then this error is disappear:

dsn := "root:xxx@tcp(127.0.0.1:3306)/xxx?charset=utf8mb4&parseTime=True&loc=Local"
gormDb, err := gorm.Open(gormMySQL.Open(dsn))
writeConn := gormDb.WriteDB
tx := db.Begin()
    defer func() {
        tx.Commit()
    }()
_, err := tx.Raw("sql clause").Rows

I want to know why use writeConn.Raw("sql clause").Rows directly cause this error? does it open a new connection to mysql db and how can I close this single connection ?

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