case.out

PostgreSQL 8.1.4的源码 适用于Linux下的开源数据库系统

--
-- CASE
-- Test the case statement
--
CREATE TABLE CASE_TBL (
  i integer,
  f double precision
);
CREATE TABLE CASE2_TBL (
  i integer,
  j integer
);
INSERT INTO CASE_TBL VALUES (1, 10.1);
INSERT INTO CASE_TBL VALUES (2, 20.2);
INSERT INTO CASE_TBL VALUES (3, -30.3);
INSERT INTO CASE_TBL VALUES (4, NULL);
INSERT INTO CASE2_TBL VALUES (1, -1);
INSERT INTO CASE2_TBL VALUES (2, -2);
INSERT INTO CASE2_TBL VALUES (3, -3);
INSERT INTO CASE2_TBL VALUES (2, -4);
INSERT INTO CASE2_TBL VALUES (1, NULL);
INSERT INTO CASE2_TBL VALUES (NULL, -6);
--
-- Simplest examples without tables
--
SELECT '3' AS "One",
  CASE
    WHEN 1 < 2 THEN 3
  END AS "Simple WHEN";
 One | Simple WHEN 
-----+-------------
 3   |           3
(1 row)

SELECT '<NULL>' AS "One",
  CASE
    WHEN 1 > 2 THEN 3
  END AS "Simple default";
  One   | Simple default 
--------+----------------
 <NULL> |               
(1 row)

SELECT '3' AS "One",
  CASE
    WHEN 1 < 2 THEN 3
    ELSE 4
  END AS "Simple ELSE";
 One | Simple ELSE 
-----+-------------
 3   |           3
(1 row)

SELECT '4' AS "One",
  CASE
    WHEN 1 > 2 THEN 3
    ELSE 4
  END AS "ELSE default";
 One | ELSE default 
-----+--------------
 4   |            4
(1 row)

SELECT '6' AS "One",
  CASE
    WHEN 1 > 2 THEN 3
    WHEN 4 < 5 THEN 6
    ELSE 7
  END AS "Two WHEN with default";
 One | Two WHEN with default 
-----+-----------------------
 6   |                     6
(1 row)

-- Constant-expression folding shouldn't evaluate unreachable subexpressions
SELECT CASE WHEN 1=0 THEN 1/0 WHEN 1=1 THEN 1 ELSE 2/0 END;
 case 
------
    1
(1 row)

SELECT CASE 1 WHEN 0 THEN 1/0 WHEN 1 THEN 1 ELSE 2/0 END;
 case 
------
    1
(1 row)

-- However we do not currently suppress folding of potentially
-- reachable subexpressions
SELECT CASE WHEN i > 100 THEN 1/0 ELSE 0 END FROM case_tbl;
ERROR:  division by zero
-- Test for cases involving untyped literals in test expression
SELECT CASE 'a' WHEN 'a' THEN 1 ELSE 2 END;
 case 
------
    1
(1 row)

--
-- Examples of targets involving tables
--
SELECT '' AS "Five",
  CASE
    WHEN i >= 3 THEN i
  END AS ">= 3 or Null"
  FROM CASE_TBL;
 Five | >= 3 or Null 
------+--------------
      |             
      |             
      |            3
      |            4
(4 rows)

SELECT '' AS "Five",
  CASE WHEN i >= 3 THEN (i + i)
       ELSE i
  END AS "Simplest Math"
  FROM CASE_TBL;
 Five | Simplest Math 
------+---------------
      |             1
      |             2
      |             6
      |             8
(4 rows)

SELECT '' AS "Five", i AS "Value",
  CASE WHEN (i < 0) THEN 'small'
       WHEN (i = 0) THEN 'zero'
       WHEN (i = 1) THEN 'one'
       WHEN (i = 2) THEN 'two'
       ELSE 'big'
  END AS "Category"
  FROM CASE_TBL;
 Five | Value | Category 
------+-------+----------
      |     1 | one
      |     2 | two
      |     3 | big
      |     4 | big
(4 rows)

SELECT '' AS "Five",
  CASE WHEN ((i < 0) or (i < 0)) THEN 'small'
       WHEN ((i = 0) or (i = 0)) THEN 'zero'
       WHEN ((i = 1) or (i = 1)) THEN 'one'
       WHEN ((i = 2) or (i = 2)) THEN 'two'
       ELSE 'big'
  END AS "Category"
  FROM CASE_TBL;
 Five | Category 
------+----------
      | one
      | two
      | big
      | big
(4 rows)

--
-- Examples of qualifications involving tables
--
--
-- NULLIF() and COALESCE()
-- Shorthand forms for typical CASE constructs
--  defined in the SQL92 standard.
--
SELECT * FROM CASE_TBL WHERE COALESCE(f,i) = 4;
 i | f 
---+---
 4 |  
(1 row)

SELECT * FROM CASE_TBL WHERE NULLIF(f,i) = 2;
 i | f 
---+---
(0 rows)

SELECT COALESCE(a.f, b.i, b.j)
  FROM CASE_TBL a, CASE2_TBL b;
 coalesce 
----------
     10.1
     20.2
    -30.3
        1
     10.1
     20.2
    -30.3
        2
     10.1
     20.2
    -30.3
        3
     10.1
     20.2
    -30.3
        2
     10.1
     20.2
    -30.3
        1
     10.1
     20.2
    -30.3
       -6
(24 rows)

SELECT *
  FROM CASE_TBL a, CASE2_TBL b
  WHERE COALESCE(a.f, b.i, b.j) = 2;
 i | f | i | j  
---+---+---+----
 4 |   | 2 | -2
 4 |   | 2 | -4
(2 rows)

SELECT '' AS Five, NULLIF(a.i,b.i) AS "NULLIF(a.i,b.i)",
  NULLIF(b.i, 4) AS "NULLIF(b.i,4)"
  FROM CASE_TBL a, CASE2_TBL b;
 five | NULLIF(a.i,b.i) | NULLIF(b.i,4) 
------+-----------------+---------------
      |                 |             1
      |               2 |             1
      |               3 |             1
      |               4 |             1
      |               1 |             2
      |                 |             2
      |               3 |             2
      |               4 |             2
      |               1 |             3
      |               2 |             3
      |                 |             3
      |               4 |             3
      |               1 |             2
      |                 |             2
      |               3 |             2
      |               4 |             2
      |                 |             1
      |               2 |             1
      |               3 |             1
      |               4 |             1
      |               1 |              
      |               2 |              
      |               3 |              
      |               4 |              
(24 rows)

SELECT '' AS "Two", *
  FROM CASE_TBL a, CASE2_TBL b
  WHERE COALESCE(f,b.i) = 2;
 Two | i | f | i | j  
-----+---+---+---+----
     | 4 |   | 2 | -2
     | 4 |   | 2 | -4
(2 rows)

--
-- Examples of updates involving tables
--
UPDATE CASE_TBL
  SET i = CASE WHEN i >= 3 THEN (- i)
                ELSE (2 * i) END;
SELECT * FROM CASE_TBL;
 i  |   f   
----+-------
  2 |  10.1
  4 |  20.2
 -3 | -30.3
 -4 |      
(4 rows)

UPDATE CASE_TBL
  SET i = CASE WHEN i >= 2 THEN (2 * i)
                ELSE (3 * i) END;
SELECT * FROM CASE_TBL;
  i  |   f   
-----+-------
   4 |  10.1
   8 |  20.2
  -9 | -30.3
 -12 |      
(4 rows)

UPDATE CASE_TBL
  SET i = CASE WHEN b.i >= 2 THEN (2 * j)
                ELSE (3 * j) END
  FROM CASE2_TBL b
  WHERE j = -CASE_TBL.i;
SELECT * FROM CASE_TBL;
  i  |   f   
-----+-------
   8 |  20.2
  -9 | -30.3
 -12 |      
  -8 |  10.1
(4 rows)

--
-- Clean up
--
DROP TABLE CASE_TBL;
DROP TABLE CASE2_TBL;