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1994.4.66
by Marisa Plumb
adding control flow functions |
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Control Flow Functions
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======================
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1994.4.67
by Marisa Plumb
CASE operator |
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There are four control flow functions: |
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* CASE
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* IF/ELSE
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* IFNULL
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* NULLIF
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2194.5.3
by Andrew Hutchings
Markup fixes |
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Control flow functions return a value for each row processed, which represents the result of the comparison or condition specified. They can be used in ``SELECT``, ``WHERE``, ``ORDER BY``, and ``GROUP BY`` statements. |
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There are two basic examples of the ``CASE`` statment:
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1. ::
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1994.4.68
by Marisa Plumb
edits to CASE function |
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CASE value WHEN [compare_value] THEN result [WHEN [compare_value] THEN result ...] [ELSE result] END |
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1994.4.67
by Marisa Plumb
CASE operator |
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2194.5.3
by Andrew Hutchings
Markup fixes |
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In this version, result is returned when value is equal to compare_value. If nothing is matched, the result after ``ELSE`` is returned, or ``NULL`` is returned if there is no ``ELSE`` part. |
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1994.4.67
by Marisa Plumb
CASE operator |
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2194.5.3
by Andrew Hutchings
Markup fixes |
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2. ::
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1994.4.68
by Marisa Plumb
edits to CASE function |
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CASE WHEN [condition] THEN result [WHEN [condition] THEN result ...] [ELSE result] END |
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2194.5.3
by Andrew Hutchings
Markup fixes |
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In this version, if [condition] is true, result is returned. If nothing is matched, the result after ``ELSE`` is returned, or ``NULL`` is returned if there is no ``ELSE`` part. |
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1994.4.68
by Marisa Plumb
edits to CASE function |
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2194.5.3
by Andrew Hutchings
Markup fixes |
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When [condition] is for equal comparison (=), this example syntax returns the same result as the first example. |