DB 复习

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create function one()
returns integer as
$$
select 1 as result;
$$
language sql;

create function add_int(integer,integer)
returns integer as
$$
select $1 + $2;
$$
language sql;

-- t4
create function write_to_temp(id integer, name varchar(20))
RETURNS integer AS
$$
insert into temp(id, name) VALUES($1, $2)
returning id;
$$
language sql VOLATILE;

create or replace function delete_from_temp(id integer)
returns integer as
$$
delete from temp where id = $1
returning id;
$$
language sql VOLATILE;

create or replace function update_temp(id integer,name varchar(20))
returns integer as
$$
update temp set name = $2 where id = $1
returning id;
$$
language sql VOLATILE;

create or replace function select_temp(id integer)
returns varchar(20) as
$$
select name from temp where id = $1;
$$
language sql VOLATILE;

-- t1
create function say(varchar(20))
returns varchar(20) as
$$
select $1;
$$
language sql;

-- t5
create type combo_nation as (nationkey integer,nationname char(25));
create or replace function get_nations(region_name varchar(20))
returns setof combo_nation as
$$
select n.n_nationkey, n.n_name from nation n, region r
where r.r_name = $1 and r.r_regionkey = n.n_regionkey;
$$
language sql;

select count(o_orderkey)
from orders
where cast (o_orderdate as varchar(20)) like '1997%';

create or replace function get_order_count(varchar(20))
returns bigint as
$$
select count(o_orderkey)
from orders
where cast (o_orderdate as varchar(20)) like $1||'%';
$$
language sql;

-- t2
create or replace function mypower(a double precision, b double precision)
returns double precision as
$$
select a^b
$$
language sql;

-- t3
create or replace function mymod(a integer, b integer)
returns integer as
$$
select a%b
$$
language sql;

-- t6
create function square(numeric[2],numeric)
returns numeric[2] as
$$
select array[$1[0]^2,$1[1]^2];
$$
language sql IMMUTABLE;

create function mean(numeric[2])
returns numeric as
$$
select ($1[0]^2+$1[1]^2)/2
$$
language sql IMMUTABLE;

create aggregate square_mean (numeric[2])
(
sfunc = square,
stype = numeric[],
finalfunc = mean
);

-- t7
create type mytype as (id integer,name char(25), age integer);
create function setmytype(integer, char(25),integer)
returns id as
$$
set copy.id = $1,
$$
Python连接数据库执行操作
import psycopg2
conn = psycopg2.connect(database="testdb", user="postgres", password="password", host="127.0.0.1", port="5432")
print "Opened database successfully"
cur = conn.cursor()
cur.execute(“…")
conn.commit()
cur.close()
conn.close()