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'
WHEN8 THEN 'DELETE'
WHEN4 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. |
