golang+presto查询在数据平台中ad hoc查询

先贴一下GitHub地址：https://github.com/derekennui/presto-go-sql

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)
}