select_distinct.out

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

--
-- SELECT_DISTINCT
--
--
-- awk '{print $3;}' onek.data | sort -n | uniq
--
SELECT DISTINCT two FROM tmp;
 two 
-----
   0
   1
(2 rows)

--
-- awk '{print $5;}' onek.data | sort -n | uniq
--
SELECT DISTINCT ten FROM tmp;
 ten 
-----
   0
   1
   2
   3
   4
   5
   6
   7
   8
   9
(10 rows)

--
-- awk '{print $16;}' onek.data | sort -d | uniq
--
SELECT DISTINCT string4 FROM tmp;
 string4 
---------
 AAAAxx
 HHHHxx
 OOOOxx
 VVVVxx
(4 rows)

--
-- awk '{print $3,$16,$5;}' onek.data | sort -d | uniq |
-- sort +0n -1 +1d -2 +2n -3
--
SELECT DISTINCT two, string4, ten
   FROM tmp
   ORDER BY two using <, string4 using <, ten using <;
 two | string4 | ten 
-----+---------+-----
   0 | AAAAxx  |   0
   0 | AAAAxx  |   2
   0 | AAAAxx  |   4
   0 | AAAAxx  |   6
   0 | AAAAxx  |   8
   0 | HHHHxx  |   0
   0 | HHHHxx  |   2
   0 | HHHHxx  |   4
   0 | HHHHxx  |   6
   0 | HHHHxx  |   8
   0 | OOOOxx  |   0
   0 | OOOOxx  |   2
   0 | OOOOxx  |   4
   0 | OOOOxx  |   6
   0 | OOOOxx  |   8
   0 | VVVVxx  |   0
   0 | VVVVxx  |   2
   0 | VVVVxx  |   4
   0 | VVVVxx  |   6
   0 | VVVVxx  |   8
   1 | AAAAxx  |   1
   1 | AAAAxx  |   3
   1 | AAAAxx  |   5
   1 | AAAAxx  |   7
   1 | AAAAxx  |   9
   1 | HHHHxx  |   1
   1 | HHHHxx  |   3
   1 | HHHHxx  |   5
   1 | HHHHxx  |   7
   1 | HHHHxx  |   9
   1 | OOOOxx  |   1
   1 | OOOOxx  |   3
   1 | OOOOxx  |   5
   1 | OOOOxx  |   7
   1 | OOOOxx  |   9
   1 | VVVVxx  |   1
   1 | VVVVxx  |   3
   1 | VVVVxx  |   5
   1 | VVVVxx  |   7
   1 | VVVVxx  |   9
(40 rows)

--
-- awk '{print $2;}' person.data |
-- awk '{if(NF!=1){print $2;}else{print;}}' - emp.data |
-- awk '{if(NF!=1){print $2;}else{print;}}' - student.data |
-- awk 'BEGIN{FS="      ";}{if(NF!=1){print $5;}else{print;}}' - stud_emp.data |
-- sort -n -r | uniq
--
SELECT DISTINCT p.age FROM person* p ORDER BY age using >;
 age 
-----
  98
  88
  78
  68
  60
  58
  50
  48
  40
  38
  34
  30
  28
  25
  24
  23
  20
  19
  18
   8
(20 rows)

--
-- Also, some tests of IS DISTINCT FROM, which doesn't quite deserve its
-- very own regression file.
--
CREATE TEMP TABLE disttable (f1 integer);
INSERT INTO DISTTABLE VALUES(1);
INSERT INTO DISTTABLE VALUES(2);
INSERT INTO DISTTABLE VALUES(3);
INSERT INTO DISTTABLE VALUES(NULL);
-- basic cases
SELECT f1, f1 IS DISTINCT FROM 2 as "not 2" FROM disttable;
 f1 | not 2 
----+-------
  1 | t
  2 | f
  3 | t
    | t
(4 rows)

SELECT f1, f1 IS DISTINCT FROM NULL as "not null" FROM disttable;
 f1 | not null 
----+----------
  1 | t
  2 | t
  3 | t
    | f
(4 rows)

SELECT f1, f1 IS DISTINCT FROM f1 as "false" FROM disttable;
 f1 | false 
----+-------
  1 | f
  2 | f
  3 | f
    | f
(4 rows)

SELECT f1, f1 IS DISTINCT FROM f1+1 as "not null" FROM disttable;
 f1 | not null 
----+----------
  1 | t
  2 | t
  3 | t
    | f
(4 rows)

-- check that optimizer constant-folds it properly
SELECT 1 IS DISTINCT FROM 2 as "yes";
 yes 
-----
 t
(1 row)

SELECT 2 IS DISTINCT FROM 2 as "no";
 no 
----
 f
(1 row)

SELECT 2 IS DISTINCT FROM null as "yes";
 yes 
-----
 t
(1 row)

SELECT null IS DISTINCT FROM null as "no";
 no 
----
 f
(1 row)