304 lines
6.0 KiB
Plaintext
304 lines
6.0 KiB
Plaintext
--
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-- CASE
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-- Test the case statement
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--
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CREATE TABLE CASE_TBL (
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i integer,
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f double precision
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);
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CREATE TABLE CASE2_TBL (
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i integer,
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j integer
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);
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INSERT INTO CASE_TBL VALUES (1, 10.1);
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INSERT INTO CASE_TBL VALUES (2, 20.2);
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INSERT INTO CASE_TBL VALUES (3, -30.3);
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INSERT INTO CASE_TBL VALUES (4, NULL);
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INSERT INTO CASE2_TBL VALUES (1, -1);
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INSERT INTO CASE2_TBL VALUES (2, -2);
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INSERT INTO CASE2_TBL VALUES (3, -3);
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INSERT INTO CASE2_TBL VALUES (2, -4);
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INSERT INTO CASE2_TBL VALUES (1, NULL);
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INSERT INTO CASE2_TBL VALUES (NULL, -6);
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--
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-- Simplest examples without tables
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--
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SELECT '3' AS "One",
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CASE
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WHEN 1 < 2 THEN 3
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END AS "Simple WHEN";
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One | Simple WHEN
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-----+-------------
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3 | 3
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(1 row)
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SELECT '<NULL>' AS "One",
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CASE
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WHEN 1 > 2 THEN 3
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END AS "Simple default";
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One | Simple default
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--------+----------------
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<NULL> |
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(1 row)
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SELECT '3' AS "One",
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CASE
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WHEN 1 < 2 THEN 3
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ELSE 4
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END AS "Simple ELSE";
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One | Simple ELSE
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-----+-------------
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3 | 3
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(1 row)
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SELECT '4' AS "One",
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CASE
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WHEN 1 > 2 THEN 3
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ELSE 4
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END AS "ELSE default";
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One | ELSE default
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-----+--------------
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4 | 4
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(1 row)
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SELECT '6' AS "One",
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CASE
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WHEN 1 > 2 THEN 3
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WHEN 4 < 5 THEN 6
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ELSE 7
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END AS "Two WHEN with default";
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One | Two WHEN with default
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-----+-----------------------
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6 | 6
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(1 row)
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-- Constant-expression folding shouldn't evaluate unreachable subexpressions
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SELECT CASE WHEN 1=0 THEN 1/0 WHEN 1=1 THEN 1 ELSE 2/0 END;
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case
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------
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1
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(1 row)
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SELECT CASE 1 WHEN 0 THEN 1/0 WHEN 1 THEN 1 ELSE 2/0 END;
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case
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------
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1
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(1 row)
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-- However we do not currently suppress folding of potentially
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-- reachable subexpressions
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SELECT CASE WHEN i > 100 THEN 1/0 ELSE 0 END FROM case_tbl;
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ERROR: division by zero
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-- Test for cases involving untyped literals in test expression
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SELECT CASE 'a' WHEN 'a' THEN 1 ELSE 2 END;
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case
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------
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1
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(1 row)
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--
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-- Examples of targets involving tables
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--
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SELECT '' AS "Five",
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CASE
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WHEN i >= 3 THEN i
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END AS ">= 3 or Null"
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FROM CASE_TBL;
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Five | >= 3 or Null
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------+--------------
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| 3
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| 4
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(4 rows)
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SELECT '' AS "Five",
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CASE WHEN i >= 3 THEN (i + i)
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ELSE i
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END AS "Simplest Math"
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FROM CASE_TBL;
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Five | Simplest Math
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------+---------------
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| 1
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| 2
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| 6
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| 8
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(4 rows)
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SELECT '' AS "Five", i AS "Value",
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CASE WHEN (i < 0) THEN 'small'
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WHEN (i = 0) THEN 'zero'
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WHEN (i = 1) THEN 'one'
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WHEN (i = 2) THEN 'two'
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ELSE 'big'
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END AS "Category"
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FROM CASE_TBL;
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Five | Value | Category
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------+-------+----------
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| 1 | one
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| 2 | two
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| 3 | big
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| 4 | big
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(4 rows)
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SELECT '' AS "Five",
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CASE WHEN ((i < 0) or (i < 0)) THEN 'small'
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WHEN ((i = 0) or (i = 0)) THEN 'zero'
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WHEN ((i = 1) or (i = 1)) THEN 'one'
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WHEN ((i = 2) or (i = 2)) THEN 'two'
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ELSE 'big'
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END AS "Category"
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FROM CASE_TBL;
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Five | Category
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------+----------
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| one
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| two
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| big
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| big
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(4 rows)
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--
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-- Examples of qualifications involving tables
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--
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--
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-- NULLIF() and COALESCE()
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-- Shorthand forms for typical CASE constructs
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-- defined in the SQL92 standard.
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--
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SELECT * FROM CASE_TBL WHERE COALESCE(f,i) = 4;
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i | f
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---+---
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4 |
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(1 row)
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SELECT * FROM CASE_TBL WHERE NULLIF(f,i) = 2;
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i | f
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---+---
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(0 rows)
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SELECT COALESCE(a.f, b.i, b.j)
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FROM CASE_TBL a, CASE2_TBL b;
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coalesce
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----------
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10.1
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20.2
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-30.3
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1
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10.1
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20.2
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-30.3
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2
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10.1
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20.2
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-30.3
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3
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10.1
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20.2
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-30.3
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2
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10.1
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20.2
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-30.3
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1
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10.1
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20.2
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-30.3
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-6
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(24 rows)
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SELECT *
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FROM CASE_TBL a, CASE2_TBL b
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WHERE COALESCE(a.f, b.i, b.j) = 2;
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i | f | i | j
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---+---+---+----
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4 | | 2 | -2
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4 | | 2 | -4
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(2 rows)
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SELECT '' AS Five, NULLIF(a.i,b.i) AS "NULLIF(a.i,b.i)",
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NULLIF(b.i, 4) AS "NULLIF(b.i,4)"
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FROM CASE_TBL a, CASE2_TBL b;
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five | NULLIF(a.i,b.i) | NULLIF(b.i,4)
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------+-----------------+---------------
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| | 1
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| 2 | 1
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| 3 | 1
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| 4 | 1
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| 1 | 2
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| | 2
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| 3 | 2
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| 4 | 2
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| 1 | 3
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| 2 | 3
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| | 3
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| 4 | 3
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| 1 | 2
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| | 2
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| 3 | 2
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| 4 | 2
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| | 1
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| 2 | 1
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| 3 | 1
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| 4 | 1
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| 1 |
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| 2 |
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| 3 |
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| 4 |
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(24 rows)
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SELECT '' AS "Two", *
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FROM CASE_TBL a, CASE2_TBL b
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WHERE COALESCE(f,b.i) = 2;
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Two | i | f | i | j
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-----+---+---+---+----
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| 4 | | 2 | -2
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| 4 | | 2 | -4
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(2 rows)
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--
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-- Examples of updates involving tables
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--
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UPDATE CASE_TBL
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SET i = CASE WHEN i >= 3 THEN (- i)
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ELSE (2 * i) END;
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SELECT * FROM CASE_TBL;
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i | f
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----+-------
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2 | 10.1
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4 | 20.2
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-3 | -30.3
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-4 |
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(4 rows)
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UPDATE CASE_TBL
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SET i = CASE WHEN i >= 2 THEN (2 * i)
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ELSE (3 * i) END;
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SELECT * FROM CASE_TBL;
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i | f
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-----+-------
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4 | 10.1
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8 | 20.2
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-9 | -30.3
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-12 |
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(4 rows)
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UPDATE CASE_TBL
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SET i = CASE WHEN b.i >= 2 THEN (2 * j)
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ELSE (3 * j) END
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FROM CASE2_TBL b
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WHERE j = -CASE_TBL.i;
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SELECT * FROM CASE_TBL;
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i | f
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-----+-------
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8 | 20.2
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-9 | -30.3
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-12 |
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-8 | 10.1
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(4 rows)
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--
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-- Clean up
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--
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DROP TABLE CASE_TBL;
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DROP TABLE CASE2_TBL;
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