Add a simple tutorial for cockroachdb

Marcin K · Marcin K · commit 63f26f6fb99a · 2019-11-29T08:00:00.000+01:00
diff --git a/database/cockroachdb/TUTORIAL.md b/database/cockroachdb/TUTORIAL.md
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+# CockroachDB tutorial for beginners (insecure cluster)
+
+## Create/configure database
+
+First, let's start a local cluster - follow step 1. and 2. from [the docs](https://www.cockroachlabs.com/docs/stable/start-a-local-cluster.html#step-1-start-the-first-node).
+
+Once you have it, create a database. Here I am going to create a database called `example`.
+Our user here is `cockroach`. We are not going to use a password, since it's not supported for insecure cluster.
+```
+cockroach sql --insecure --host=localhost:26257
+```
+```
+CREATE DATABASE example;
+CREATE USER IF NOT EXISTS cockroach;
+GRANT ALL ON DATABASE example TO cockroach;
+```
+
+When using Migrate CLI we need to pass to database URL. Let's export it to a variable for convienience:
+```
+export COCKROACHDB_URL=cockroachdb://cockroach:@localhost:26257/example?sslmode=disable
+```
+`sslmode=disable` means that the connection with our database will not be encrypted. This is needed to connect to an insecure node.
+
+**NOTE:** Do not use COCKROACH_URL as a variable name here, it's already in use for discrete parameters and you may run into connection problems. For more info check out [docs](https://www.cockroachlabs.com/docs/stable/connection-parameters.html#connect-using-discrete-parameters).
+
+You can find further description of database URLs [here](README.md#database-urls).
+
+## Create migrations
+Let's create a table called `users`:
+```
+migrate create -ext sql -dir db/migrations -seq create_users_table
+```
+If there were no errors, we should have two files available under `db/migrations` folder:
+- 000001_create_users_table.down.sql
+- 000001_create_users_table.up.sql
+
+Note the `sql` extension that we provided.
+
+In the `.up.sql` file let's create the table:
+```
+CREATE TABLE IF NOT EXISTS example.users
+(
+   user_id INT PRIMARY KEY,
+   username VARCHAR (50) UNIQUE NOT NULL,
+   password VARCHAR (50) NOT NULL,
+   email VARCHAR (300) UNIQUE NOT NULL
+);
+```
+And in the `.down.sql` let's delete it:
+```
+DROP TABLE IF EXISTS example.users;
+```
+By adding `IF EXISTS/IF NOT EXISTS` we are making migrations idempotent - you can read more about idempotency in [getting started](GETTING_STARTED.md#create-migrations)
+
+## Run migrations
+```
+migrate -database ${COCKROACHDB_URL} -path db/migrations up
+```
+Let's check if the table was created properly by running `cockroach sql --insecure --host=localhost:26257 -e "show columns from example.users;"`.
+The output you are supposed to see:
+```
+  column_name |  data_type   | is_nullable | column_default | generation_expression |                   indices                    | is_hidden
++-------------+--------------+-------------+----------------+-----------------------+----------------------------------------------+-----------+
+  user_id     | INT8         |    false    | NULL           |                       | {primary,users_username_key,users_email_key} |   false
+  username    | VARCHAR(50)  |    false    | NULL           |                       | {users_username_key}                         |   false
+  password    | VARCHAR(50)  |    false    | NULL           |                       | {}                                           |   false
+  email       | VARCHAR(300) |    false    | NULL           |                       | {users_email_key}                            |   false
+(4 rows)
+```
+Now let's check if running reverse migration also works:
+```
+migrate -database ${COCKROACHDB_URL} -path db/migrations down
+```
+Make sure to check if your database changed as expected in this case as well.
+
+## Database transactions
+
+To show database transactions usage, let's create another set of migrations by running:
+```
+migrate create -ext sql -dir db/migrations -seq add_mood_to_users
+```
+Again, it should create for us two migrations files:
+- 000002_add_mood_to_users.down.sql
+- 000002_add_mood_to_users.up.sql
+
+In Cockroach, when we want our queries to be done in a transaction, we need to wrap it with `BEGIN` and `COMMIT` commands, similar to PostgreSQL.
+In our example, we are going to add a column to our database that can only accept enumerable values or NULL.
+Migration up:
+```
+BEGIN;
+
+ALTER TABLE example.users ADD COLUMN mood STRING;
+ALTER TABLE example.users ADD CONSTRAINT check_mood CHECK (mood IN ('happy', 'sad', 'neutral'));
+
+COMMIT;
+```
+Migration down:
+```
+ALTER TABLE example.users DROP COLUMN mood;
+```
+
+Now we can run our new migration and check the database:
+```
+migrate -database ${COCKROACHDB_URL} -path db/migrations up
+cockroach sql --insecure --host=localhost:26257 -e "show columns from example.users;"
+```
+Expected output:
+```
+  column_name |  data_type   | is_nullable | column_default | generation_expression |                   indices                    | is_hidden  
++-------------+--------------+-------------+----------------+-----------------------+----------------------------------------------+-----------+
+  user_id     | INT8         |    false    | NULL           |                       | {primary,users_username_key,users_email_key} |   false    
+  username    | VARCHAR(50)  |    false    | NULL           |                       | {users_username_key}                         |   false    
+  password    | VARCHAR(50)  |    false    | NULL           |                       | {}                                           |   false    
+  email       | VARCHAR(300) |    false    | NULL           |                       | {users_email_key}                            |   false    
+  mood        | STRING       |    true     | NULL           |                       | {}                                           |   false    
+(5 rows)
+```
+
+## Optional: Run migrations within your Go app
+Here is a very simple app running migrations for the above configuration:
+```
+import (
+	"log"
+
+	"github.com/golang-migrate/migrate/v4"
+	_ "github.com/golang-migrate/migrate/v4/database/cockroachdb"
+	_ "github.com/golang-migrate/migrate/v4/source/file"
+)
+
+func main() {
+	m, err := migrate.New(
+		"file://db/migrations",
+		"cockroachdb://cockroach:@localhost:26257/example?sslmode=disable")
+	if err != nil {
+		log.Fatal(err)
+	}
+	if err := m.Up(); err != nil {
+		log.Fatal(err)
+	}
+}
+```
+You can find details [here](README.md#use-in-your-go-project)
