http://www.alberton.info/postgresql_meta_info.html
PostgreSQL INFORMATION_SCHEMA
Following my tutorial on how to extract meta informations from Firebird SQL, I'm now going to show how to retrieve the same informations from PostgreSQL, using the INFORMATION_SCHEMA (available since PostgreSQL 7.4) and with system catalogs (pg_class, pg_user, pg_view, etc).
NB: as you probably know, you can list tables/indices/sequences/views from the command line with the \d{t|i|s|v} command, but here I want to show how to extract these informations using standard SQL queries.
Test data
We need a few sample tables, indices and views to test the following queries, so let's create them. We also create a sample TRIGGER and a function.
-- sample data to test PostgreSQL INFORMATION_SCHEMA
-- TABLE TEST
CREATE TABLE TEST (
TEST_NAME CHAR(30) NOT NULL,
TEST_ID INTEGER DEFAULT '0' NOT NULL,
TEST_DATE TIMESTAMP NOT NULL
);
ALTER TABLE TEST ADD CONSTRAINT PK_TEST PRIMARY KEY (TEST_ID);
-- TABLE TEST2 with some CONSTRAINTs and an INDEX
CREATE TABLE TEST2 (
ID INTEGER NOT NULL,
FIELD1 INTEGER,
FIELD2 CHAR(15),
FIELD3 VARCHAR(50),
FIELD4 INTEGER,
FIELD5 INTEGER,
ID2 INTEGER NOT NULL
);
ALTER TABLE TEST2 ADD CONSTRAINT PK_TEST2 PRIMARY KEY (ID2);
ALTER TABLE TEST2 ADD CONSTRAINT TEST2_FIELD1ID_IDX UNIQUE (ID, FIELD1);
ALTER TABLE TEST2 ADD CONSTRAINT TEST2_FIELD4_IDX UNIQUE (FIELD4);
CREATE INDEX TEST2_FIELD5_IDX ON TEST2(FIELD5);
-- TABLE NUMBERS
CREATE TABLE NUMBERS (
NUMBER INTEGER DEFAULT '0' NOT NULL,
EN CHAR(100) NOT NULL,
FR CHAR(100) NOT NULL
);
-- TABLE NEWTABLE
CREATE TABLE NEWTABLE (
ID INT DEFAULT 0 NOT NULL,
SOMENAME VARCHAR (12),
SOMEDATE TIMESTAMP NOT NULL
);
ALTER TABLE NEWTABLE ADD CONSTRAINT PKINDEX_IDX PRIMARY KEY (ID);
CREATE SEQUENCE NEWTABLE_SEQ INCREMENT 1 START 1;
-- VIEW on TEST
CREATE VIEW "testview"(
TEST_NAME,
TEST_ID,
TEST_DATE
) AS
SELECT *
FROM TEST
WHERE TEST_NAME LIKE 't%';
-- VIEW on NUMBERS
CREATE VIEW "numbersview"(
NUMBER,
TRANS_EN,
TRANS_FR
) AS
SELECT *
FROM NUMBERS
WHERE NUMBER > 100;
-- TRIGGER on NEWTABLE
CREATE FUNCTION add_stamp() RETURNS OPAQUE AS '
BEGIN
IF (NEW.somedate IS NULL OR NEW.somedate = 0) THEN
NEW.somedate := CURRENT_TIMESTAMP;
RETURN NEW;
END IF;
END;
' LANGUAGE 'plpgsql';
CREATE TRIGGER ADDCURRENTDATE
BEFORE INSERT OR UPDATE
ON newtable FOR EACH ROW
EXECUTE PROCEDURE add_stamp();
List TABLEs
Here's the query that will return the names of the tables defined in the current database:
SELECT relname
FROM pg_class
WHERE relname !~ '^(pg_|sql_)'
AND relkind = 'r'; -- using INFORMATION_SCHEMA: SELECT table_name FROM information_schema.tables WHERE table_type = 'BASE TABLE' AND table_schema NOT IN ('pg_catalog', 'information_schema'); List VIEWs
Here's the query that will return the names of the VIEWs defined in the current database:
-- with postgresql 7.2:
SELECT viewname
FROM pg_views
WHERE viewname !~ '^pg_';
-- with postgresql 7.4 and later:
SELECT viewname
FROM pg_views
WHERE schemaname NOT IN
('pg_catalog', 'information_schema')
AND viewname !~ '^pg_';
-- using INFORMATION_SCHEMA:
SELECT table_name
FROM information_schema.tables
WHERE table_type = 'VIEW'
AND table_schema NOT IN
('pg_catalog', 'information_schema')
AND table_name !~ '^pg_';
-- or
SELECT table_name
FROM information_schema.views
WHERE table_schema NOT IN ('pg_catalog', 'information_schema')
AND table_name !~ '^pg_';
List users
SELECT usename
FROM pg_user;
List INDICES
Here's the query that will return the names of the INDICES defined in the TEST2 table. Unfortunately I have no idea how to extract them from the INFORMATION_SCHEMA. If you do, please let me know.
NB: the CONSTRAINTs are not listed
SELECT relname
FROM pg_class
WHERE oid IN (
SELECT indexrelid
FROM pg_index, pg_class
WHERE pg_class.relname='test2'
AND pg_class.oid=pg_index.indrelid
AND indisunique != 't'
AND indisprimary != 't'
);
List CONSTRAINTs
Here's the query that will return the names of the CONSTRAINTs defined in the TEST2 table:
SELECT relname
FROM pg_class
WHERE oid IN (
SELECT indexrelid
FROM pg_index, pg_class
WHERE pg_class.relname='test2'
AND pg_class.oid=pg_index.indrelid
AND ( indisunique = 't'
OR indisprimary = 't'
)
);
-- with INFORMATION_SCHEMA:
SELECT constraint_name, constraint_type
FROM information_schema.table_constraints
WHERE table_name = 'test2';
List table fields
Here's the query that will return the names of the fields of the TEST2 table:
SELECT a.attname
FROM pg_class c, pg_attribute a, pg_type t
WHERE c.relname = 'test2'
AND a.attnum > 0
AND a.attrelid = c.oid
AND a.atttypid = t.oid
-- with INFORMATION_SCHEMA:
SELECT column_name
FROM information_schema.columns
WHERE table_name = 'test2';
If you want some more info about the field definitions, you can retrieve a larger subset of the fields available in the schema:
SELECT a.attnum AS ordinal_position,
a.attname AS column_name,
t.typname AS data_type,
a.attlen AS character_maximum_length,
a.atttypmod AS modifier,
a.attnotnull AS notnull,
a.atthasdef AS hasdefault
FROM pg_class c,
pg_attribute a,
pg_type t
WHERE c.relname = 'test2'
AND a.attnum > 0
AND a.attrelid = c.oid
AND a.atttypid = t.oid
ORDER BY a.attnum;
-- with INFORMATION_SCHEMA:
SELECT ordinal_position,
column_name,
data_type,
column_default,
is_nullable,
character_maximum_length,
numeric_precision
FROM information_schema.columns
WHERE table_name = 'test2'
ORDER BY ordinal_position;
List sequences
A SEQUENCE is an object that automatically generate sequence numbers. A SEQUENCE is often used to ensure a unique value in a PRIMARY KEY that must uniquely identify the associated row.
SELECT relname
FROM pg_class
WHERE relkind = 'S'
AND relnamespace IN (
SELECT oid
FROM pg_namespace
WHERE nspname NOT LIKE 'pg_%'
AND nspname != 'information_schema'
);
List TRIGGERs
SELECT trg.tgname AS trigger_name
FROM pg_trigger trg, pg_class tbl
WHERE trg.tgrelid = tbl.oid
AND tbl.relname !~ '^pg_';
-- or
SELECT tgname AS trigger_name
FROM pg_trigger
WHERE tgname !~ '^pg_';
-- with INFORMATION_SCHEMA:
SELECT DISTINCT trigger_name
FROM information_schema.triggers
WHERE trigger_schema NOT IN
('pg_catalog', 'information_schema');
List only the triggers for a given table:
SELECT trg.tgname AS trigger_name
FROM pg_trigger trg, pg_class tbl
WHERE trg.tgrelid = tbl.oid
AND tbl.relname = 'newtable';
-- with INFORMATION_SCHEMA:
SELECT DISTINCT trigger_name
FROM information_schema.triggers
WHERE event_object_table = 'newtable'
AND trigger_schema NOT IN
('pg_catalog', 'information_schema');
Show more informations about the trigger definitions:
SELECT trg.tgname AS trigger_name,
tbl.relname AS table_name,
p.proname AS function_name,
CASE trg.tgtype & cast(2 as int2)
WHEN 0 THEN 'AFTER'
ELSE 'BEFORE'
END AS trigger_type,
CASE trg.tgtype & cast(28 as int2)
WHEN 16 THEN 'UPDATE'
WHEN 8 THEN 'DELETE'
WHEN 4 THEN 'INSERT'
WHEN 20 THEN 'INSERT, UPDATE'
WHEN 28 THEN 'INSERT, UPDATE, DELETE'
WHEN 24 THEN 'UPDATE, DELETE'
WHEN 12 THEN 'INSERT, DELETE'
END AS trigger_event
FROM pg_trigger trg,
pg_class tbl,
pg_proc p
WHERE trg.tgrelid = tbl.oid
AND trg.tgfoid = p.oid
AND tbl.relname !~ '^pg_';
-- with INFORMATION_SCHEMA:
SELECT *
FROM information_schema.triggers
WHERE trigger_schema NOT IN
('pg_catalog', 'information_schema');
List FUNCTIONs
SELECT proname
FROM pg_proc pr,
pg_type tp
WHERE tp.oid = pr.prorettype
AND pr.proisagg = FALSE
AND tp.typname <> 'trigger'
AND pr.pronamespace IN (
SELECT oid
FROM pg_namespace
WHERE nspname NOT LIKE 'pg_%'
AND nspname != 'information_schema'
);
-- with INFORMATION_SCHEMA:
SELECT routine_name
FROM information_schema.routines
WHERE specific_schema NOT IN
('pg_catalog', 'information_schema')
AND type_udt_name != 'trigger';
Albe Laurenz sent me the following function that is even more informative: for a function name and schema, it selects the position in the argument list, the direction, the name and the data-type of each argument. This procedure requires PostgreSQL 8.1 or later.
CREATE OR REPLACE FUNCTION public.function_args(
IN funcname character varying,
IN schema character varying,
OUT pos integer,
OUT direction character,
OUT argname character varying,
OUT datatype character varying)
RETURNS SETOF RECORD AS $$DECLARE
rettype character varying;
argtypes oidvector;
allargtypes oid[];
argmodes "char"[];
argnames text[];
mini integer;
maxi integer;
BEGIN
/* get object ID of function */
SELECT INTO rettype, argtypes, allargtypes, argmodes, argnames
CASE
WHEN pg_proc.proretset
THEN 'setof ' || pg_catalog.format_type(pg_proc.prorettype, NULL)
ELSE pg_catalog.format_type(pg_proc.prorettype, NULL) END,
pg_proc.proargtypes,
pg_proc.proallargtypes,
pg_proc.proargmodes,
pg_proc.proargnames
FROM pg_catalog.pg_proc
JOIN pg_catalog.pg_namespace
ON (pg_proc.pronamespace = pg_namespace.oid)
WHERE pg_proc.prorettype <> 'pg_catalog.cstring':
g_catalog.regtype
AND (pg_proc.proargtypes[0] IS NULL
OR pg_proc.proargtypes[0] <> 'pg_catalog.cstring':
g_catalog.regtype)
AND NOT pg_proc.proisagg
AND pg_proc.proname = funcname
AND pg_namespace.nspname = schema
AND pg_catalog.pg_function_is_visible(pg_proc.oid);
/* bail out if not found */
IF NOT FOUND THEN
RETURN;
END IF;
/* return a row for the return value */
pos = 0;
direction = 'o'::char;
argname = 'RETURN VALUE';
datatype = rettype;
RETURN NEXT;
/* unfortunately allargtypes is NULL if there are no OUT parameters */
IF allargtypes IS NULL THEN
mini = array_lower(argtypes, 1); maxi = array_upper(argtypes, 1);
ELSE
mini = array_lower(allargtypes, 1); maxi = array_upper(allargtypes, 1);
END IF;
IF maxi < mini THEN RETURN; END IF;
/* loop all the arguments */
FOR i IN mini .. maxi LOOP
pos = i - mini + 1;
IF argnames IS NULL THEN
argname = NULL;
ELSE
argname = argnames
;
END IF;
IF allargtypes IS NULL THEN
direction = 'i'::char;
datatype = pg_catalog.format_type(argtypes, NULL);
ELSE
direction = argmodes;
datatype = pg_catalog.format_type(allargtypes, NULL);
END IF;
RETURN NEXT;
END LOOP;
RETURN;
END;$$ LANGUAGE plpgsql STABLE STRICT SECURITY INVOKER;
COMMENT ON FUNCTION public.function_args(character varying, character
varying)
IS $$For a function name and schema, this procedure selects for each
argument the following data:
- position in the argument list (0 for the return value)
- direction 'i', 'o', or 'b'
- name (NULL if not defined)
- data type$$;
What else?
If you'd like to see some other example queries, or have some comments and/or suggestions, just drop me a mail (you can find my address in the footer of this page) and I'll add them to this list.
HTH.
