Starting with PostgreSQL in the Windows Instructional Lab

Are you using PostgreSQL on your own computer?

If so, then some of these instructions may not apply to you. Make sure you have read the instructions on installing software for working from home, and in particular that you understand how to adapt these instructions to a personal PostgreSQL installation.


To help you gain experience with multiple database management systems, we will use the open-source PostgreSQL DBMS along with SQL Server in CSE 444. Instead of running on a central server such as IISQLSRV, you will run PostgreSQL on your personal computer with data stored in your private files.

For the second and third projects you'll run PostgreSQL on the Windows computers in the undergrad labs. This page is a brief introduction; if you would like to learn more about PostgreSQL, here is a more detailed tutorial. (We recommend skipping the tutorial's material on the SQL language, especially joins; refer to your book and the lecture notes instead.)

Getting a PostgreSQL command prompt

Unlike SQL Server, PostgreSQL is not usually used through a graphical interface. Rather, the server and client tools are typically accessed from a command line. To get a command shell that is set up to run these tools on the Lab machines, download and run the PostgreSQL shell launcher script, 444shell.cmd. This script sets the command search PATH variable to include the PostgreSQL commands, and the Java CLASSPATH variable to include the PostgreSQL and SQL Server JDBC drivers (needed for project 2).

To test that the script has set up the tools paths correctly, type psql -? at the prompt, and hit Enter. You should see a usage message like the following:

psql is the PostgreSQL interactive terminal.


Creating a data folder

Both SQL Server and PostgreSQL store databases in ordinary files within the filesystem. On IISQLSRV, all the data files are located in a single directory which you cannot access. When you use PostgreSQL, however, you will create a data folder just for yourself. To create the data files, do the following:

  1. Create the folder where you want to put the data files. We recommend putting this folder either on the local computer's C: or D: drive, for fast access, or somewhere that is accessible to all Windows Lab machines, such as your Unix home folder Z:, to avoid needing to back up the data folder whenever you log out from the machine.

    On the rest of this page we'll assume you use the C:\pgsql_data folder. IMPORTANT: per the above, this folder is lost on system shutdown in the Labs!
  2. Open a PostgreSQL shell using the environment script above.
  3. Run the initdb command to create the data files:
    > initdb -D C:\pgsql_data

Starting and stopping PostgreSQL

To start PostgreSQL, run the pg_ctl start command by choosing Start→Run, giving the name of the data folder you created earlier:

> "C:\Program Files\PostgreSQL\8.4\bin\pg_ctl.exe" start -D C:\pgsql_data

Remember: don't type this into the PostgreSQL shell you got from 444shell.cmd, type it into the Start→Run menu.

This will pop up a shell window that displays server starting among other messages. When done, you can stop PostgreSQL either by hitting Ctrl-C in the shell window, or by using the pg_ctl stop command:

> "C:\Program Files\PostgreSQL\8.4\bin\pg_ctl.exe" stop -D C:\pgsql_data

On Windows Vista and 7, you can type these commands into the Start menu's search bar, rather than the Start→Run box.

Creating a PostgreSQL database

Just as in SQL Server, your tables must be placed in a database, which you must create. To create a database named my_database, run the createdb command from a PostgreSQL shell that you got from 444shell.cmd:

> createdb my_database

Note that, unlike SQL Server, PostgreSQL is case-sensitive when looking up database and table names. However, PostgreSQL automatically lowercases all names given in SQL code, so the case-sensitivity only affects non-SQL code that uses the database name, such as:

In such code, always spell the database name exactly as you created it, respecting case.

Running queries with psql

To run SQL queries on SQL Server, you use SQL Server Management Studio. In PostgreSQL, you use the psql utility. Once PostgreSQL is running, you can run psql by opening a PostgreSQL shell and typing

> psql my_database

where my_database is the name of the database you want to use. (If you omit the database name, psql defaults to accessing the database with the same name as your username.)

When psql opens, you will see a message like this:

psql (8.4.4)
Type "help" for help.


The line alice=# is the prompt for SQL statements which are sent to the database server, or non-SQL commands interpreted by psql. Here, "alice" is the name of the database.

To exit psql, type \q and press Enter:

alice=# \q


Note that there is no semicolon after \q; this is required because \q and other backslash-quoted commands are not part of SQL and are interpreted by psql, rather than the PostgreSQL server.

Entering queries

Type in a SQL statement to run it. SQL statements can be split across multiple lines; to send the SQL statement to the server, end the statement with a semicolon and press Enter. Depending on the command, psql will either respond with a confirmation message:

alice=# DELETE FROM hw1_data
alice-# WHERE name='name';

or display the results of the query in a table:

alice=# SELECT * FROM hw1_data;
  name  | discount | month | price
 bar1   | 15%      | apr   | 19
 bar8   | 15%      | apr   | 19
 gizmo3 | 15%      | apr   | 19
 gizmo7 | 15%      | apr   | 19
 mouse1 | 15%      | apr   | 19
 bar1   | 15%      | aug   | 19
 bar8   | 15%      | aug   | 19
 gizmo3 | 15%      | aug   | 19
 gizmo7 | 15%      | aug   | 19
 mouse1 | 15%      | aug   | 19
 bar1   | 33%      | dec   | 19
 bar8   | 33%      | dec   | 19
 gizmo3 | 33%      | dec   | 19
 (426 rows)

If the result table is too large to fit in the shell window, it will be shown one window-ful at a time; press Enter to go on to the next window, until the end.

If you make a mistake while typing in a query, you can use the up-arrow and down-arrow keys on the keyboard to move between previously entered lines, which you can then edit and resubmit.

Running queries from an SQL file

As in SQL Server Management Studio, you can use psql to run SQL code from an external file as well as from interactive input. This can be done with the \i psql command:

alice=# \i 'query.sql'

Note that psql follows PostgreSQL in allowing backslash escape sequences in character strings. This means that an absolute pathname like D:\subdir\query.sql must be written either by doubling the backslashes, as in 'D:\\subdir\\query.sql', or turning them into forward slashes, as in 'D:/subdir/query.sql'.

Alternativeley, you can run psql with the query file directly from the shell:

> psql -f "query.sql" my_database

Saving query output to a file

You can send the output of queries to a file instead of (not in addition to) your console with the \o psql command:

alice=# \o 'query_output.txt'

Note that the SQL code of queries will not be saved to the file. To stop saving query output and send it to your console again, use the same command, but omit the filename:

alice=# \o

Copying data from a file into a table

You can import data from a file on the client computer into an existing database table using the \copy psql command:

alice=# \copy hw1_data from 'hw1_data.txt'

For the first homework, there is an SQL script that imports the data from the data file into a new table hw1_data. This script uses the \copy command internally.

Getting info about tables and database objects

In SQL Server Management Studio, you can view information about the columns, constraints, and indices on a table through the tree view on the left side of the Management Studio window. To get similar information in PostgreSQL, you use the \d psql command:

alice=# \d hw1_data
           Table "public.hw1_data"
  Column  |         Type          | Modifiers
 name     | character varying(50) |
 discount | character varying(50) |
 month    | character varying(50) |
 price    | character varying(50) |

Getting info about query plans

In Management Studio, you can request that the estimated plan for a query be displayed by choosing the Query→Display Estimated Execution Plan menu item. The equivalent in PostgreSQL is the EXPLAIN statement of SQL, which produces a plain-text representation of the physical query plan. (Instead of EXPLAIN, SQL Server has the SET SHOWPLAN and SET STATISTICS families of statements, but the syntax is different.)

Here is an example of the use of EXPLAIN on a simple query:

alice=# EXPLAIN SELECT * FROM hw1_data;
                        QUERY PLAN
 Seq Scan on hw1_data  (cost=0.00..7.26 rows=426 width=17)
(1 row)

Management Studio also lets you view the actual plan for a query once the query has been executed, by turning on the Query→Include Actual Execution Plan menu option before running the query. The equivalent function in PostgreSQL is the EXPLAIN ANALYZE variation of the EXPLAIN statement:

                        QUERY PLAN
 Seq Scan on hw1_data  (cost=0.00..7.26 rows=426 width=17)
(actual time=0.011..0.183 rows=426 loops=1)
 Total runtime: 0.390 ms
(2 rows)