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package main
import (
"database/sql"
"fmt"
"log"
"math"
"math/rand"
sqlite "github.com/mattn/go-sqlite3"
)
// Computes x^y
func pow(x, y int64) int64 {
return int64(math.Pow(float64(x), float64(y)))
}
// Computes the bitwise exclusive-or of all its arguments
func xor(xs ...int64) int64 {
var ret int64
for _, x := range xs {
ret ^= x
}
return ret
}
// Returns a random number. It's actually deterministic here because
// we don't seed the RNG, but it's an example of a non-pure function
// from SQLite's POV.
func getrand() int64 {
return rand.Int63()
}
// Computes the standard deviation of a GROUPed BY set of values
type stddev struct {
xs []int64
// Running average calculation
sum int64
n int64
}
func newStddev() *stddev { return &stddev{} }
func (s *stddev) Step(x int64) {
s.xs = append(s.xs, x)
s.sum += x
s.n++
}
func (s *stddev) Done() float64 {
mean := float64(s.sum) / float64(s.n)
var sqDiff []float64
for _, x := range s.xs {
sqDiff = append(sqDiff, math.Pow(float64(x)-mean, 2))
}
var dev float64
for _, x := range sqDiff {
dev += x
}
dev /= float64(len(sqDiff))
return math.Sqrt(dev)
}
func main() {
sql.Register("sqlite3_custom", &sqlite.SQLiteDriver{
ConnectHook: func(conn *sqlite.SQLiteConn) error {
if err := conn.RegisterFunc("pow", pow, true); err != nil {
return err
}
if err := conn.RegisterFunc("xor", xor, true); err != nil {
return err
}
if err := conn.RegisterFunc("rand", getrand, false); err != nil {
return err
}
if err := conn.RegisterAggregator("stddev", newStddev, true); err != nil {
return err
}
return nil
},
})
db, err := sql.Open("sqlite3_custom", ":memory:")
if err != nil {
log.Fatal("Failed to open database:", err)
}
defer db.Close()
var i int64
err = db.QueryRow("SELECT pow(2,3)").Scan(&i)
if err != nil {
log.Fatal("POW query error:", err)
}
fmt.Println("pow(2,3) =", i) // 8
err = db.QueryRow("SELECT xor(1,2,3,4,5,6)").Scan(&i)
if err != nil {
log.Fatal("XOR query error:", err)
}
fmt.Println("xor(1,2,3,4,5) =", i) // 7
err = db.QueryRow("SELECT rand()").Scan(&i)
if err != nil {
log.Fatal("RAND query error:", err)
}
fmt.Println("rand() =", i) // pseudorandom
_, err = db.Exec("create table foo (department integer, profits integer)")
if err != nil {
log.Fatal("Failed to create table:", err)
}
_, err = db.Exec("insert into foo values (1, 10), (1, 20), (1, 45), (2, 42), (2, 115)")
if err != nil {
log.Fatal("Failed to insert records:", err)
}
rows, err := db.Query("select department, stddev(profits) from foo group by department")
if err != nil {
log.Fatal("STDDEV query error:", err)
}
defer rows.Close()
for rows.Next() {
var dept int64
var dev float64
if err := rows.Scan(&dept, &dev); err != nil {
log.Fatal(err)
}
fmt.Printf("dept=%d stddev=%f\n", dept, dev)
}
if err := rows.Err(); err != nil {
log.Fatal(err)
}
}
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