Add code snippets.

go.mod

@@ -0,0 +1,3 @@
+module github.com/kaz/isucon9-prep
+
+require github.com/jmoiron/sqlx v1.2.0

go.sum

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+github.com/go-sql-driver/mysql v1.4.0/go.mod h1:zAC/RDZ24gD3HViQzih4MyKcchzm+sOG5ZlKdlhCg5w=
+github.com/jmoiron/sqlx v1.2.0 h1:41Ip0zITnmWNR/vHV+S4m+VoUivnWY5E4OJfLZjCJMA=
+github.com/jmoiron/sqlx v1.2.0/go.mod h1:1FEQNm3xlJgrMD+FBdI9+xvCksHtbpVBBw5dYhBSsks=
+github.com/lib/pq v1.0.0/go.mod h1:5WUZQaWbwv1U+lTReE5YruASi9Al49XbQIvNi/34Woo=
+github.com/mattn/go-sqlite3 v1.9.0/go.mod h1:FPy6KqzDD04eiIsT53CuJW3U88zkxoIYsOqkbpncsNc=

samples/sql/go.mod

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+module sql
+
+require (
+	github.com/go-sql-driver/mysql v1.4.1
+	github.com/jmoiron/sqlx v1.2.0
+	github.com/lib/pq v1.2.0 // indirect
+	github.com/mattn/go-sqlite3 v1.11.0 // indirect
+)

samples/sql/go.sum

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+github.com/go-sql-driver/mysql v1.4.0/go.mod h1:zAC/RDZ24gD3HViQzih4MyKcchzm+sOG5ZlKdlhCg5w=
+github.com/go-sql-driver/mysql v1.4.1 h1:g24URVg0OFbNUTx9qqY1IRZ9D9z3iPyi5zKhQZpNwpA=
+github.com/go-sql-driver/mysql v1.4.1/go.mod h1:zAC/RDZ24gD3HViQzih4MyKcchzm+sOG5ZlKdlhCg5w=
+github.com/jmoiron/sqlx v1.2.0 h1:41Ip0zITnmWNR/vHV+S4m+VoUivnWY5E4OJfLZjCJMA=
+github.com/jmoiron/sqlx v1.2.0/go.mod h1:1FEQNm3xlJgrMD+FBdI9+xvCksHtbpVBBw5dYhBSsks=
+github.com/lib/pq v1.0.0/go.mod h1:5WUZQaWbwv1U+lTReE5YruASi9Al49XbQIvNi/34Woo=
+github.com/lib/pq v1.2.0/go.mod h1:5WUZQaWbwv1U+lTReE5YruASi9Al49XbQIvNi/34Woo=
+github.com/mattn/go-sqlite3 v1.9.0/go.mod h1:FPy6KqzDD04eiIsT53CuJW3U88zkxoIYsOqkbpncsNc=
+github.com/mattn/go-sqlite3 v1.11.0/go.mod h1:FPy6KqzDD04eiIsT53CuJW3U88zkxoIYsOqkbpncsNc=

samples/sql/main.go

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+package main
+
+import (
+	crand "crypto/rand"
+	"encoding/binary"
+	"fmt"
+	"log"
+	"math/rand"
+	"time"
+
+	_ "github.com/go-sql-driver/mysql"
+	"github.com/jmoiron/sqlx"
+)
+
+var (
+	db *sqlx.DB
+)
+
+// User ...
+type User struct {
+	Name string `json:"name" db:"name"`
+	Age  int64  `json:"age" db:"age"`
+}
+
+func init() {
+	seedBuf := make([]byte, 8)
+	crand.Read(seedBuf)
+	rand.Seed(int64(binary.LittleEndian.Uint64(seedBuf)))
+
+	dbHost := "127.0.0.1"
+
+	dbPort := "3306"
+
+	dbUser := "root"
+
+	dbPassword := ":" + "114514YJsnpi1919$"
+
+	dsn := fmt.Sprintf("%s%s@tcp(%s:%s)/isubata?parseTime=true&loc=Local&charset=utf8mb4",
+		dbUser, dbPassword, dbHost, dbPort)
+
+	log.Printf("Connecting to db: %q", dsn)
+
+	tmpdb, err := sqlx.Connect("mysql", dsn)
+
+	if err != nil {
+		log.Printf("Error: %q", err)
+		return
+	}
+
+	db = tmpdb
+
+	for {
+		err := db.Ping()
+		if err == nil {
+			break
+		}
+		log.Println(err)
+		time.Sleep(time.Second * 3)
+	}
+
+	db.SetMaxOpenConns(20)
+	db.SetConnMaxLifetime(5 * time.Minute)
+	log.Printf("Succeeded to connect db.")
+}
+
+// db.Exec
+func createUser() {
+	schema := `CREATE TABLE IF NOT EXISTS user (
+		name text,
+		age integer);`
+
+	result, err := db.Exec(schema)
+
+	if err != nil {
+		log.Printf("Error: %q", err)
+	} else {
+		log.Printf("Result: %q", result)
+	}
+}
+
+// db.MustExec
+func insertUser() {
+	sentence := `INSERT INTO user (name, age) VALUES ("david", 114514);`
+	db.MustExec(sentence)
+}
+
+// db.Queryx
+func selectUserQueryx() {
+	sentence := `SELECT * FROM user;`
+
+	rows, err := db.Queryx(sentence)
+
+	if err != nil {
+		log.Printf("Error: %q", err)
+		return
+	}
+
+	for rows.Next() {
+		var u User
+		err = rows.StructScan(&u)
+
+		if err != nil {
+			log.Printf("Error: %q", err)
+			return
+		}
+
+		fmt.Println(u)
+	}
+}
+
+// db.Select
+func selectUserSelect() {
+	sentence := `SELECT * FROM user;`
+
+	us := []User{}
+
+	err := db.Select(&us, sentence)
+
+	if err != nil {
+		log.Printf("Error: %q", err)
+		return
+	}
+
+	for _, u := range us {
+		fmt.Println(u)
+	}
+}
+
+func nPlus1() {
+
+}
+
+func nPlus1EagerLoading() {
+
+}
+
+func nPlus1Join() {
+
+}
+
+func main() {
+	createUser()
+
+	insertUser()
+
+	selectUserQueryx()
+
+	selectUserSelect()
+}