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|
--
-- 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;
|