先贴一下GitHub地址：github.com/derekennui/…
presto作为分布式计算引擎，因为其提供了跨数据源查询功能，以及内存计算优秀的性能，在我司应用到了很多场景。由于我司以golang为主，所以实现了一个简陋的presto sql查询工具。 通常情况下golang查询需要预先定好struct，再传入指针，对于ad hoc查询显然是不满足的，所以只能将其转化为json格式。 比如我们数据库中数据如下：
PersonID LastName FirstName Address City
1 White Clover 305 - 14th Ave. S. Suite 3B Seattle
2 Wilman Kala Keskuskatu 45 Helsinki
传入sql：
select * from mysql.test.Persons
得到的返回结果：
[{"address":"305 - 14th Ave. S. Suite 3B","city":"Seattle","firstname":"Clover","lastname":"White","personid":1}, {"address":"Keskuskatu 45","city":"Helsinki","firstname":"Kala","lastname":"Wilman","personid":2}]
代码如下：
package main
import (
"database/sql"
"encoding/json"
"fmt"
"reflect"
"github.com/go-sql-driver/mysql"
_ "github.com/prestodb/presto-go-client/presto"
)
func main() {
prestoUrl := "http://user@localhost:8080?catalog=mysql&schema=test"
sqlExe := "select * from mysql.test.Persons"
content, _ := ExePrestoSqlQuery(prestoUrl, sqlExe)
fmt.Println("query result : ", string(content))
}
type jsonNullInt64 struct {
sql.NullInt64
}
func (v jsonNullInt64) MarshalJSON() ([]byte, error) {
if !v.Valid {
return json.Marshal(nil)
}
return json.Marshal(v.Int64)
}
type jsonNullFloat64 struct {
sql.NullFloat64
}
func (v jsonNullFloat64) MarshalJSON() ([]byte, error) {
if !v.Valid {
return json.Marshal(nil)
}
return json.Marshal(v.Float64)
}
type jsonNullTime struct {
mysql.NullTime
}
func (v jsonNullTime) MarshalJSON() ([]byte, error) {
if !v.Valid {
return json.Marshal(nil)
}
return json.Marshal(v.Time)
}
var jsonNullInt64Type = reflect.TypeOf(jsonNullInt64{})
var jsonNullFloat64Type = reflect.TypeOf(jsonNullFloat64{})
var jsonNullTimeType = reflect.TypeOf(jsonNullTime{})
var nullInt64Type = reflect.TypeOf(sql.NullInt64{})
var nullFloat64Type = reflect.TypeOf(sql.NullFloat64{})
var nullTimeType = reflect.TypeOf(mysql.NullTime{})
func ExePrestoSqlQuery(prestoUrl string, sqlExe string) ([]byte, error) {
db, err := sql.Open("presto", prestoUrl)
if err != nil {
return nil, fmt.Errorf("can't connect to presto error: %v", err)
}
rows, err := db.Query(sqlExe)
defer rows.Close()
columns, err := rows.Columns()
if err != nil {
return nil, fmt.Errorf("column error: %v", err)
}
ct, err := rows.ColumnTypes()
if err != nil {
return nil, fmt.Errorf("column type error: %v", err)
}
types := make([]reflect.Type, len(ct))
for i, tp := range ct {
st := tp.ScanType()
if st == nil {
return nil, fmt.Errorf("scantype is null for column: %v", err)
}
switch st {
case nullInt64Type:
types[i] = jsonNullInt64Type
case nullFloat64Type:
types[i] = jsonNullFloat64Type
case nullTimeType:
types[i] = jsonNullTimeType
default:
types[i] = st
}
}
values := make([]interface{}, len(ct))
var slice []map[string]interface{}
for rows.Next() {
for i := range values {
values[i] = reflect.New(types[i]).Interface()
}
err = rows.Scan(values...)
if err != nil {
return nil, fmt.Errorf("failed to scan values: %v", err)
}
data := make(map[string]interface{})
for i, v := range values {
data[columns[i]] = v
}
slice = append(slice, data)
}
return json.Marshal(slice)
}
