Postgres SQL CRUD example

algorithms/math/FastPowering/README.md

@@ -2,7 +2,6 @@
 
 **The power of a number** says how many times to use the number in a multiplication.
 
-
 ## Naive Algorithm Complexity
 
 To find `a` raised to the power `b` we multiply `a` to itself, `b` times. That is, `a^b = a * a * a * ... * a` (`b` occurrences of `a`).
@@ -24,8 +23,7 @@ X^Y = X^(Y/2) * X^(Y/2)
 For **odd** `Y`:
 
 ```text
-X^Y = X^(Y//2) * X^(Y//2) * X
-where Y//2 is result of division of Y by 2 without reminder.
+X^Y = X^(Y/2) * X^(Y/2) * X
 ```
 
 **For example**

beginner-programs/Postgres-CRUD/postgres.go

@@ -0,0 +1,182 @@
+package main
+
+import (
+	"database/sql"
+	"fmt"
+	"log"
+	"time"
+
+	"github.com/lib/pq"
+	_ "github.com/lib/pq"
+)
+
+const (
+	host     = "localhost"
+	port     = 5432
+	user     = "postgres"
+	password = "example"
+	dbname   = "pq-demo"
+)
+
+type Book struct {
+	ID              int
+	Name            string
+	Author          string
+	PublicationDate time.Time
+	Pages           int
+}
+
+func createTable() {
+	query := `
+	CREATE TABLE books
+	(
+	 id serial NOT NULL,
+	 name character varying NOT NULL,
+	 author character varying,
+	 pages integer,
+	 publication_date date,
+	 CONSTRAINT pk_books PRIMARY KEY (id )
+	)
+	WITH (
+	 OIDS=FALSE
+	);
+	ALTER TABLE books
+	 OWNER TO postgres;`
+
+	if _, err := db.Exec(query); err != nil {
+		log.Fatal(err)
+	}
+}
+
+func dropTable() {
+	query := `DROP TABLE books;`
+
+	if _, err := db.Exec(query); err != nil {
+		log.Fatal(err)
+	}
+}
+
+func getBook(bookID int) (Book, error) {
+	res := Book{}
+
+	var id int
+	var name string
+	var author string
+	var pages int
+	var publicationDate pq.NullTime
+
+	err := db.QueryRow(`SELECT id, name, author, pages, publication_date FROM books where id = $1`, bookID).Scan(&id, &name, &author, &pages, &publicationDate)
+	if err == nil {
+		res = Book{ID: id, Name: name, Author: author, Pages: pages, PublicationDate: publicationDate.Time}
+	}
+
+	return res, err
+}
+
+func getAllBooks() ([]Book, error) {
+	books := []Book{}
+
+	rows, err := db.Query(`SELECT id, name, author, pages, publication_date FROM books order by id`)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+
+	for rows.Next() {
+		var id int
+		var name string
+		var author string
+		var pages int
+		var publicationDate pq.NullTime
+
+		err = rows.Scan(&id, &name, &author, &pages, &publicationDate)
+		if err != nil {
+			return books, err
+		}
+
+		currentBook := Book{ID: id, Name: name, Author: author, Pages: pages}
+		if publicationDate.Valid {
+			currentBook.PublicationDate = publicationDate.Time
+		}
+
+		books = append(books, currentBook)
+	}
+
+	return books, err
+}
+
+func insertBook(name, author string, pages int, publicationDate time.Time) (int, error) {
+	var bookID int
+	err := db.QueryRow(`INSERT INTO books(name, author, pages, publication_date) VALUES($1, $2, $3, $4) RETURNING id`, name, author, pages, publicationDate).Scan(&bookID)
+
+	if err != nil {
+		return 0, err
+	}
+
+	fmt.Printf("Last inserted ID: %v\n", bookID)
+	return bookID, err
+}
+
+func updateBook(id int, name, author string, pages int, publicationDate time.Time) (int, error) {
+	res, err := db.Exec(`UPDATE books set name=$1, author=$2, pages=$3, publication_date=$4 where id=$5 RETURNING id`, name, author, pages, publicationDate, id)
+	if err != nil {
+		return 0, err
+	}
+
+	rowsUpdated, err := res.RowsAffected()
+	if err != nil {
+		return 0, err
+	}
+
+	return int(rowsUpdated), err
+}
+
+func removeBook(bookID int) (int, error) {
+	res, err := db.Exec(`delete from books where id = $1`, bookID)
+	if err != nil {
+		return 0, err
+	}
+
+	rowsDeleted, err := res.RowsAffected()
+	if err != nil {
+		return 0, err
+	}
+
+	return int(rowsDeleted), nil
+}
+
+var db *sql.DB
+
+func main() {
+	psqlInfo := fmt.Sprintf("host=%s port=%d user=%s "+
+		"password=%s dbname=%s sslmode=disable",
+		host, port, user, password, dbname)
+
+	var err error
+	db, err = sql.Open("postgres", psqlInfo)
+	if err != nil {
+		panic(err)
+	}
+	// defer db.Close()
+
+	err = db.Ping()
+	if err != nil {
+		panic(err)
+	}
+
+	fmt.Println("Successfully connected!")
+
+	createTable()
+
+	insertBook("Hello World", "Author", 100, time.Now())
+
+	fmt.Println(getAllBooks())
+
+	updateBook(1, "Hello World 2!", "Author 2", 205, time.Now())
+
+	fmt.Println(getBook(1))
+
+	removeBook(1)
+
+	dropTable()
+}