165 lines
3.3 KiB
SQL
165 lines
3.3 KiB
SQL
--
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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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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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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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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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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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-- 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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SELECT CASE 1 WHEN 0 THEN 1/0 WHEN 1 THEN 1 ELSE 2/0 END;
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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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-- 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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--
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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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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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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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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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--
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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 SQL standard.
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--
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SELECT * FROM CASE_TBL WHERE COALESCE(f,i) = 4;
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SELECT * FROM CASE_TBL WHERE NULLIF(f,i) = 2;
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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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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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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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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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--
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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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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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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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--
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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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