case.sql

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";

SELECT '<NULL>' AS "One",
  CASE
    WHEN 1 > 2 THEN 3
  END AS "Simple default";

SELECT '3' AS "One",
  CASE
    WHEN 1 < 2 THEN 3
    ELSE 4
  END AS "Simple ELSE";

SELECT '4' AS "One",
  CASE
    WHEN 1 > 2 THEN 3
    ELSE 4
  END AS "ELSE default";

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

-- 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;
SELECT CASE 1 WHEN 0 THEN 1/0 WHEN 1 THEN 1 ELSE 2/0 END;

-- 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;

-- Test for cases involving untyped literals in test expression
SELECT CASE 'a' WHEN 'a' THEN 1 ELSE 2 END;

--
-- Examples of targets involving tables
--

SELECT '' AS "Five",
  CASE
    WHEN i >= 3 THEN i
  END AS ">= 3 or Null"
  FROM CASE_TBL;

SELECT '' AS "Five",
  CASE WHEN i >= 3 THEN (i + i)
       ELSE i
  END AS "Simplest Math"
  FROM CASE_TBL;

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;

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;

--
-- 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;

SELECT * FROM CASE_TBL WHERE NULLIF(f,i) = 2;

SELECT COALESCE(a.f, b.i, b.j)
  FROM CASE_TBL a, CASE2_TBL b;

SELECT *
  FROM CASE_TBL a, CASE2_TBL b
  WHERE COALESCE(a.f, b.i, b.j) = 2;

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;

SELECT '' AS "Two", *
  FROM CASE_TBL a, CASE2_TBL b
  WHERE COALESCE(f,b.i) = 2;

--
-- Examples of updates involving tables
--

UPDATE CASE_TBL
  SET i = CASE WHEN i >= 3 THEN (- i)
                ELSE (2 * i) END;

SELECT * FROM CASE_TBL;

UPDATE CASE_TBL
  SET i = CASE WHEN i >= 2 THEN (2 * i)
                ELSE (3 * i) END;

SELECT * FROM CASE_TBL;

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;

--
-- Clean up
--

DROP TABLE CASE_TBL;
DROP TABLE CASE2_TBL;