179 lines
3.7 KiB
Markdown
179 lines
3.7 KiB
Markdown
---
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title: postgresql
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updated: 2021-05-04 14:58:11Z
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created: 2021-05-04 14:58:11Z
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---
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# Postgresql
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psql DBNAME USERNAME
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\d \\ list all relations
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\d tablename \\ ddl
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```bash
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sudo -u postgres CREATEUSER <username>
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sudo -u postgres CREATEDB <datebasename>
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```
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```psql
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psql# ALTER USER <username> WITH ENCRYPTED PASSWORD '<password>';
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psql# GRANT ALL PRIVILEGES ON DATABASE <databasename> to <username>;
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```
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## create csv file
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```sql
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COPY (SELECT * FROM "public".empbase) TO '/tmp/empbase.csv' WITH CSV header;
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```
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### Jupyter:
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> first install:
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> ipython-sql and psycopg2
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```jupyter
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* %load_ext sql
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* %sql postgresql://john:****@localhost/testdb
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* %%sql
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- select * from aap;
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```
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## From python program
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```python
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import psycopg2
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query = "select * from aap"
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try:
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conn = psycopg2.connect("postgres://john:qw12aap@localhost:5432/testdb")
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except psycopg2.OperationalError as e:
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print('Unable to connect!\n{0}').format(e)
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sys.exit(1)
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finally:
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print("connected")
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cur = conn.cursor()
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cur.execute(query)
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for x in cur.fetchall():
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print(x)
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cur.close()
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conn.close()
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```
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[Source PostgreSQL](https://www.postgresql.org/files/documentation/pdf/11/postgresql-11-A4.pdf)
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## Connection from Apache Spark example:
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```scala
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val driver = "org.postgresql.Driver"
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Class.forName(driver)
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val df = spark.sqlContext
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.read
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.format("jdbc")
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.options(Map("url"->"jdbc:postgresql://172.17.0.2:5432/postgres", "user"->"postgres","password"->"qw12aap","driver"->driver,"dbtable"->"company"))
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.load()
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```
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## Install Docker
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<https://hackernoon.com/dont-install-postgres-docker-pull-postgres-bee20e200198>
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<https://docs.databricks.com/spark/latest/data-sources/sql-databases.html>
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## create persistant storage location
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```bash
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mkdir -p $HOME/docker/volumes/postgres
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```
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## launch docker container
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```bash
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docker run --rm --name pg-docker -e POSTGRES_PASSWORD=docker -d -p 5432:5432 -v $HOME/docker/volumes/postgres:/var/lib/postgresql/data postgres
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```
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## connect to running container
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```bash
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docker exec -it pg-docker /bin/bash
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```
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## inside container
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```bash
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psql -h localhost -U postgres -d postgres
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```
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[Postgresql tutorial](https://www.tutorialspoint.com/postgresql)
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# notes
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psql DBNAME USERNAME
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\d \\ list all relations
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\d tablename \\ ddl
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sudo -u postgres CREATEUSER <username>
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sudo -u postgres CREATEDB <datebasename>
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psql# ALTER USER <username> WITH ENCRYPTED PASSWORD '<password>';
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psql# GRANT ALL PRIVILEGES ON DATABASE <databasename> to <username>;
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## create csv file:
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```sql
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COPY (SELECT * FROM "public".empbase) TO '/tmp/empbase.csv' WITH CSV header;
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```
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## In jupyter
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> first install:
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> ipython-sql and psycopg2
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Use:
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* %load_ext sql
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* %sql postgresql://john:****@localhost/testdb
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* %%sql
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- select * from aap;
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## From python program
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```python
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import psycopg2
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query = "select * from aap"
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try:
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conn = psycopg2.connect("postgres://john:qw12aap@localhost:5432/testdb")
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except psycopg2.OperationalError as e:
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print('Unable to connect!\n{0}').format(e)
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sys.exit(1)
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finally:
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print("connected")
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cur = conn.cursor()
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cur.execute(query)
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for x in cur.fetchall():
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print(x)
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cur.close()
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conn.close()
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```
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sources:
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https://www.postgresql.org/files/documentation/pdf/11/postgresql-11-A4.pdf
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## Connection from Apache Spark example:
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```scala
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val driver = "org.postgresql.Driver"
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Class.forName(driver)
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val df = spark.sqlContext
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.read
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.format("jdbc")
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.options(Map("url"->"jdbc:postgresql://172.17.0.2:5432/postgres", "user"->"postgres","password"->"qw12aap","driver"->driver,"dbtable"->"company"))
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.load()
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```
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