Lesson 3 - Database Administration

Prerequisites
Exercise: Create the HAWQ Tutorial Database
Exercise: Use psql for Table Operations
Summary

The HAWQ gpadmin user and other users who are granted the necessary privileges can execute SQL commands to create HAWQ databases and tables. These commands may be invoked via scripts, programs, and from the psql client utility.

This lesson introduces basic HAWQ database administration commands and tasks using psql. You will create a database and a simple table, and add data to and query the table.

Prerequisites

Ensure that you have Set Up your HAWQ Runtime Environment and that your HAWQ cluster is up and running.

Exercise: Create the HAWQ Tutorial Database

In this exercise, you use the psql command line utility to create a HAWQ database.

Start the psql subsystem:
```
gpadmin@master$ psql -d postgres
```
You enter the psql interpreter, connecting to the postgres database. postgres is a default template database created during HAWQ installation.
```
psql (8.2.15)
Type "help" for help.

postgres=# 
```
The psql prompt is the database name followed by =# or =>. =# identifies the session as that of a database superuser. The default psql prompt for a non-superuser is =>.
Create a database named hawqgsdb:
```
postgres=# CREATE DATABASE hawqgsdb;
CREATE DATABASE
```
The ; at the end of the CREATE DATABASE statement instructs psql to interpret the command. SQL commands that span multiple lines are not interpreted until the ; is entered.

Connect to the hawqgsdb database you just created:

postgres=# \c hawqgsdb
You are now connected to database "hawqgsdb" as user "gpadmin".
hawqgsdb=#

Use the psql \l meta-command to list all HAWQ databases:

hawqgsdb=# \l
                     List of databases
      Name       |  Owner  | Encoding | Access privileges 
-----------------+---------+----------+-------------------
 hawqgsdb        | gpadmin | UTF8     | 
 postgres        | gpadmin | UTF8     | 
 template0       | gpadmin | UTF8     | 
 template1       | gpadmin | UTF8     | 
(4 rows)

HAWQ creates two additional template databases during installation, template0 and template1, as you see above. Your HAWQ cluster may list additional databases.

Exit psql:
```
hawqgsdb=# \q
```

Exercise: Use psql for Table Operations

You manage and access HAWQ databases and tables via the psql utility, an interactive front-end to the HAWQ database. In this exercise, you use psql to create, add data to, and query a simple HAWQ table.

Start the psql subsystem:
```
gpadmin@master$ psql -d hawqgsdb
```
The -d hawqgsdb option instructs psql to connect directly to the hawqgsdb database.
Create a table named first_tbl that has a single integer column named i:
```
hawqgsdb=# CREATE TABLE first_tbl( i int );
CREATE TABLE 
```

Display descriptive information about table first_tbl:

hawqgsdb=# \d first_tbl
Append-Only Table "public.first_tbl"
 Column |  Type   | Modifiers 
--------+---------+-----------
 i      | integer | 
Compression Type: None
Compression Level: 0
Block Size: 32768
Checksum: f
Distributed randomly

first_tbl is a table in the HAWQ public schema. first_tbl has a single integer column, was created with no compression, and is distributed randomly.

Add some data to first_tbl:
```
hawqgsdb=# INSERT INTO first_tbl VALUES(1);
INSERT 0 1
hawqgsdb=# INSERT INTO first_tbl VALUES(2);
INSERT 0 1 
```
Each INSERT command adds a row to first_tbl, the first adding a row with the value i=1, and the second, a row with the value i=2. Each INSERT also displays the number of rows added (1).
HAWQ provides several built-in functions for data manipulation. The generate_series(<start>, <end>) function generates a series of numbers beginning with <start> and finishing at <end>. Use the generate_series() HAWQ built-in function to add rows for i=3, i=4, and i=5 to first_tbl:
```
hawqgsdb=# INSERT INTO first_tbl SELECT generate_series(3, 5);
INSERT 0 3
```
This INSERTcommand uses the generate_series() built-in function to add 3 rows to first_tbl, starting with i=3 and writing and incrementing i for each new row.
Perform a query to return all rows in the first_tbl table:
```
hawqgsdb=# SELECT * FROM first_tbl;
 i  
----
  1
  2
  3
  4
  5
(5 rows)
```
The SELECT * command queries first_tbl, returning all columns and all rows. SELECT also displays the total number of rows returned in the query.
Perform a query to return column i for all rows in first_tbl where i is greater than 3:
```
hawqgsdb=# SELECT i FROM first_tbl WHERE i>3;
 i  
----
  4
  5
(2 rows)
```
The SELECT command returns the 2 rows (i=4 and i=5) in the table where i is larger than 3 and displays the value of i.
Exit the psql subsystem:
```
hawqgsdb=# \q
```
psql includes an option, -c, to run a single SQL command from the shell command line. Perform the same query you ran in Step 7 using the -c <sql-command> option:
```
gpadmin@master$ psql -d hawqgsdb -c 'SELECT i FROM first_tbl WHERE i>3'
```
Notice that you enclose the SQL command in single quotes.
Set the HAWQ PGDATABASE environment variable to identify hawqsgdb:
```
gpadmin@master$ export PGDATABASE=hawqgsdb
```
$PGDATABASE identifies the default database to which to connect when invoking the HAWQ psql command.
Re-run the query from the command line again, this time omitting the -d option:
```
gpadmin@master$ psql -c 'SELECT i FROM first_tbl WHERE i>3'
```
When no database is specified on the command line, psql attempts to connect to the database identified by $PGDATABASE.
Add the PGDATABASE setting to your .bash_profile:
```
export PGDATABASE=hawqgsdb
```

Summary

You created the database you will use in later lessons. You also created, inserted data into, and queried a simple HAWQ table usingpsql.

For information on SQL command support in HAWQ, refer to the SQL Command reference.

For detailed information on the psql subsystem, refer to the psql reference page. Commonly-used psql meta-commands are identified in the table below.

Action	Command
List databases	`\l`
List tables in current database	`\dt`
Describe a specific table	`\d <table-name>`
Execute an SQL script	`\i <script-name>`
Quit/Exit	`\q`

Lesson 4 introduces the Retail demo, a more complicated data set used in upcoming lessons. You will download and examine the data set and work files. You will also load some of the data set into HDFS.

Lesson 4: Sample Data Set and HAWQ Schemas