psql

Interactive command-line interface for HAWQ.

Synopsis

psql [<option> ...] [<dbname> [<username>]]

where:

<general options> =
    [-c '<command>' | --command '<command>'] 
    [-d <dbname> | --dbname <dbname>] 
    [-f <filename> | --file <filename>] 
    [-l | --list]
    [-v <assignment> | --set=<assignment> | --variable=<name><value>]
    [-X | --no-psqlrc]
    [-1 | --single-transaction]
    [-? | --help]  
    [--version]  
<input and output options> =
    [-a | --echo-all]
    [-e | --echo-queries]
    [-E | --echo-hidden]
    [-L <filename> | --log-file <filename>]
    [-n | --noreadline]
    [-o <filename> | --output <filename>]
    [-q | --quiet]
    [-s | --single-step]
    [-S | --single-line]
<output format options> =
    [-A | --no-align]
    [-F <separator> | --field-separator <separator>]
    [-H | --html]
    [-P <assignment> | --pset <assignment>]
    [-R <separator> | --record-separator <separator>]
    [-t | --tuples-only]
    [-T <table_options> | --table-attr     [-V | --version]
    [-x | --expanded]
<input and output options> =
    [-a | --echo-all]
    [-A | --no-align]
    [-c ’<command>’ | --command ’<command>’] 
    [-d <dbname> | --dbname <dbname>] 
    [-e | --echo-queries]
    [-E | --echo-hidden]
    [-f <filename> | --file <filename>] 
    [-F <separator> | --field-separator <separator>]
    [-H | --html]
    [-l | --list]
    [-L <filename> | --log-file <filename>]
    [-o <filename> | --output <filename>]
    [-P <assignment> | --pset <assignment>]
    [-q | --quiet]
    [-R <separator> | --record-separator <separator>]
    [-s | --single-step]
    [-S | --single-line]
    [-t | --tuples-only]
    [-T <table_options> | --table-attr     [-V | --version]
    [-x | --expanded]
<connection_options> =
    [-h <host> | --host <host>] 
    [-p <port> | -- port <port>] 
    [-U <username> | --username <username>] 
    [-W | --password]  

Description

psql is a terminal-based front-end to HAWQ. It enables you to type in queries interactively, issue them to HAWQ, and see the query results. Alternatively, input can be from a file. In addition, it provides a number of meta-commands and various shell-like features to facilitate writing scripts and automating a wide variety of tasks.

Note: HAWQ queries timeout after a period of 600 seconds. For this reason, long-running queries may appear to hang in plsql until results are processed or until the timeout period expires.

Options

General Options

echo '\x \\ SELECT * FROM foo;' | psql

Input and Output Options

Output Format Options

Connection Options

Exit Status

psql returns 0 to the shell if it finished normally, 1 if a fatal error of its own (out of memory, file not found) occurs, 2 if the connection to the server went bad and the session was not interactive, and 3 if an error occurred in a script and the variable ON_ERROR_STOP was set.

Usage

Connecting to a Database

psql is a client application for HAWQ. To connect to a database you must know the name of your target database, the host name and port number of the HAWQ master server and what database user name you want to connect as. Use the -d, -h, -p, and -U command line options, respectively, to specify these parameters to psql. If an argument is found that does not belong to any option, it will be interpreted as the database name (or the user name, if the database name is already given). Not all these options are required; there are useful defaults. If you omit the host name, psql will connect via a UNIX-domain socket to a master server on the local host, or via TCP/IP to localhost on machines that do not have UNIX-domain sockets. The default master port number is 5432. If you use a different port for the master, you must specify the port. The default database user name is your UNIX user name, as is the default database name. Note that you cannot just connect to any database under any user name. Your database administrator should have informed you about your access rights.

When the defaults are not right, you can save yourself some typing by setting any or all of the environment variables PGAPPNAME, PGDATABASE, PGHOST, PGPORT, and PGUSER to appropriate values.

It is also convenient to have a ~/.pgpass file to avoid regularly having to type in passwords. This file should reside in your home directory and contain lines of the following format:

hostname:port:database:username:password

The permissions on .pgpass must disallow any access to world or group (for example: chmod 0600 ~/.pgpass). If the permissions are less strict than this, the file will be ignored. (The file permissions are not currently checked on Microsoft Windows clients, however.)

If the connection could not be made for any reason (insufficient privileges, server is not running, etc.), psql will return an error and terminate.

Entering SQL Commands

In normal operation, psql provides a prompt with the name of the database to which psql is currently connected, followed by the string => for a regular user or =# for a superuser. For example:

testdb=>
testdb=#

At the prompt, the user may type in SQL commands. Ordinarily, input lines are sent to the server when a command-terminating semicolon is reached. An end of line does not terminate a command. Thus commands can be spread over several lines for clarity. If the command was sent and executed without error, the results of the command are displayed on the screen.

Meta-Commands

Anything you enter in psql that begins with an unquoted backslash is a psql meta-command that is processed by psql itself. These commands help make psql more useful for administration or scripting. Meta-commands are more commonly called slash or backslash commands.

The format of a psql command is the backslash, followed immediately by a command verb, then any arguments. The arguments are separated from the command verb and each other by any number of whitespace characters.

To include whitespace into an argument you may quote it with a single quote. To include a single quote into such an argument, use two single quotes. Anything contained in single quotes is furthermore subject to C-like substitutions for \n (new line), \t (tab), \digits (octal), and \xdigits (hexadecimal).

If an unquoted argument begins with a colon (:), it is taken as a psql variable and the value of the variable is used as the argument instead.

Arguments that are enclosed in backquotes (`) are taken as a command line that is passed to the shell. The output of the command (with any trailing newline removed) is taken as the argument value. The above escape sequences also apply in backquotes.

Some commands take an SQL identifier (such as a table name) as argument. These arguments follow the syntax rules of SQL: Unquoted letters are forced to lowercase, while double quotes (") protect letters from case conversion and allow incorporation of whitespace into the identifier. Within double quotes, paired double quotes reduce to a single double quote in the resulting name. For example, FOO"BAR"BAZ is interpreted as fooBARbaz, and "A weird"" name" becomes A weird" name.

Parsing for arguments stops when another unquoted backslash occurs. This is taken as the beginning of a new meta-command. The special sequence \\ (two backslashes) marks the end of arguments and continues parsing SQL commands, if any. That way SQL and psql commands can be freely mixed on a line. But in any case, the arguments of a meta-command cannot continue beyond the end of the line.

The following meta-commands are defined:

mydb=> \lo_import '/home/gpadmin/pictures/photo.xcf' 'a 
picture of me'
lo_import 152801

Patterns

The various \d commands accept a pattern parameter to specify the object name(s) to be displayed. In the simplest case, a pattern is just the exact name of the object. The characters within a pattern are normally folded to lower case, just as in SQL names; for example, \dt FOO will display the table named foo. As in SQL names, placing double quotes around a pattern stops folding to lower case. Should you need to include an actual double quote character in a pattern, write it as a pair of double quotes within a double-quote sequence; again this is in accord with the rules for SQL quoted identifiers. For example, \dt "FOO""BAR" will display the table named FOO"BAR (not foo"bar). Unlike the normal rules for SQL names, you can put double quotes around just part of a pattern, for instance \dt FOO"FOO"BAR will display the table named fooFOObar.

Within a pattern, * matches any sequence of characters (including no characters) and ? matches any single character. (This notation is comparable to UNIX shell file name patterns.) For example, \dt int* displays all tables whose names begin with int. But within double quotes, * and ? lose these special meanings and are just matched literally.

A pattern that contains a dot (.) is interpreted as a schema name pattern followed by an object name pattern. For example, \dt foo*.bar* displays all tables whose table name starts with bar that are in schemas whose schema name starts with foo. When no dot appears, then the pattern matches only objects that are visible in the current schema search path. Again, a dot within double quotes loses its special meaning and is matched literally.

Advanced users can use regular-expression notations. All regular expression special characters work as specified in the PostgreSQL documentation on regular expressions, except for . which is taken as a separator as mentioned above, * which is translated to the regular-expression notation .*, and ? which is translated to .. You can emulate these pattern characters at need by writing ? for .,(R+|) for R*, or (R|) for R?. Remember that the pattern must match the whole name, unlike the usual interpretation of regular expressions; write * at the beginning and/or end if you don’t wish the pattern to be anchored. Note that within double quotes, all regular expression special characters lose their special meanings and are matched literally. Also, the regular expression special characters are matched literally in operator name patterns (such as the argument of \do).

Whenever the pattern parameter is omitted completely, the \d commands display all objects that are visible in the current schema search path – this is equivalent to using the pattern *. To see all objects in the database, use the pattern *.*.

Advanced Features

Variables

psql provides variable substitution features similar to common UNIX command shells. Variables are simply name/value pairs, where the value can be any string of any length. To set variables, use the psql meta-command \set:

testdb=> \set foo bar

sets the variable foo to the value bar. To retrieve the content of the variable, precede the name with a colon and use it as the argument of any slash command:

testdb=> \echo :foo
bar

Note: The arguments of \set are subject to the same substitution rules as with other commands. Thus you can construct interesting references such as \set :foo 'something' and get 'soft links’ or 'variable variables’ of Perl or PHP fame, respectively. Unfortunately, there is no way to do anything useful with these constructs. On the other hand, \set bar :foo is a perfectly valid way to copy a variable.

If you call \set without a second argument, the variable is set, with an empty string as <value>. To unset (or delete) a variable, use the command \unset.

psql’s internal variable names can consist of letters, numbers, and underscores in any order and any number of them. A number of these variables are treated specially by psql. They indicate certain option settings that can be changed at run time by altering the value of the variable or represent some state of the application. Although you can use these variables for any other purpose, this is not recommended, as the program might behave unexpectedly. By convention, all specially treated variables consist of all upper-case letters (and possibly numbers and underscores). To ensure maximum compatibility in the future, avoid using such variable names for your own purposes. A list of all specially treated variables are as follows:

\set HISTFILE ~/.psql_history- :DBNAME

SQL Interpolation An additional useful feature of psql variables is that you can substitute (interpolate) them into regular SQL statements. The syntax for this is again to prepend the variable name with a colon (:).

testdb=> \set foo 'my_table'
testdb=> SELECT * FROM :foo;

would then query the table my_table. The value of the variable is copied literally, so it can even contain unbalanced quotes or backslash commands. You must make sure that it makes sense where you put it. Variable interpolation will not be performed into quoted SQL entities.

A popular application of this facility is to refer to the last inserted OID in subsequent statements to build a foreign key scenario. Another possible use of this mechanism is to copy the contents of a file into a table column. First load the file into a variable and then proceed as above.

testdb=> \set content '''' `cat my_file.txt` ''''
testdb=> INSERT INTO my_table VALUES (:content);

One problem with this approach is that my_file.txt might contain single quotes. These need to be escaped so that they don’t cause a syntax error when the second line is processed. This could be done with the program sed:

testdb=> \set content '''' `sed -e "s/'/''/g" < my_file.txt` 
''''

If you are using non-standard-conforming strings, then you’ll also need to use double backslashes. This is a bit tricky:

testdb=> \set content '''' `sed -e "s/'/''/g" -e 
's/\\/\\\\/g' < my_file.txt` ''''

Note the use of different shell quoting conventions so that neither the single quote marks nor the backslashes are special to the shell. Backslashes are still special to sed, however, so we need to double them.

Since colons may legally appear in SQL commands, the following rule applies: the character sequence ":name" is not changed unless "name" is the name of a variable that is currently set. In any case you can escape a colon with a backslash to protect it from substitution. (The colon syntax for variables is standard SQL for embedded query languages, such as ECPG. The colon syntax for array slices and type casts are HAWQ extensions, hence the conflict.)

Prompting

The prompts psql issues can be customized to your preference. The three variables PROMPT1, PROMPT2, and PROMPT3 contain strings and special escape sequences that describe the appearance of the prompt. Prompt 1 is the normal prompt that is issued when psql requests a new command. Prompt 2 is issued when more input is expected during command input because the command was not terminated with a semicolon or a quote was not closed. Prompt 3 is issued when you run an SQL COPY command and you are expected to type in the row values on the terminal.

The value of the selected prompt variable is printed literally, except where a percent sign (%) is encountered. Depending on the next character, certain other text is substituted instead. Defined substitutions are:

testdb=> \set PROMPT1 '%[%033[1;33;40m%]%n@%/%R%[%033[0m%]%#'

Command-Line Editing

psql supports the NetBSD libedit library for convenient line editing and retrieval. The command history is automatically saved when psql exits and is reloaded when psql starts up. Tab-completion is also supported, although the completion logic makes no claim to be an SQL parser. If for some reason you do not like the tab completion, you can turn it off by putting this in a file named .inputrc in your home directory:

$if psql
set disable-completion on
$endif

Environment

Files

Before starting up, psql attempts to read and execute commands from the user’s ~/.psqlrc file.

The command-line history is stored in the file ~/.psql_history.

Notes

psql only works smoothly with servers of the same version. That does not mean other combinations will fail outright, but subtle and not-so-subtle problems might come up. Backslash commands are particularly likely to fail if the server is of a different version.

Notes for Windows users

psql is built as a console application. Since the Windows console windows use a different encoding than the rest of the system, you must take special care when using 8-bit characters within psql. If psql detects a problematic console code page, it will warn you at startup. To change the console code page, two things are necessary:

Set the code page by entering:

cmd.exe /c chcp 1252

1252 is a character encoding of the Latin alphabet, used by Microsoft Windows for English and some other Western languages. If you are using Cygwin, you can put this command in /etc/profile.

Set the console font to Lucida Console, because the raster font does not work with the ANSI code page.

Examples

Start psql in interactive mode:

$ psql -p 54321 -U sally mydatabase

In psql interactive mode, spread a command over several lines of input. Notice the changing prompt:

testdb=> CREATE TABLE my_table (
testdb(>  first integer not null default 0,
testdb(>  second text)
testdb-> ;
CREATE TABLE

Look at the table definition:

testdb=> \d my_table
             Table "my_table"
 Attribute |  Type   |      Modifier
-----------+---------+--------------------
 first     | integer | not null default 0
 second    | text    |

Run psql in non-interactive mode by passing in a file containing SQL commands:

$ psql -f /home/gpadmin/test/myscript.sql