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clearer docs
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@ -581,12 +581,17 @@ the given expressions evaluate to equal. The DISTINCT ON expressions are
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interpreted using the same rules as for ORDER BY. ORDER BY is used to
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ensure that the desired row appears first.
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The DISTINCT ON expressions will be pre-appended to the ORDER BY clause.
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The DISTINCT ON expression(s) must match the leftmost ORDER BY expression(s).
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The ORDER BY clause will normally contain additional expression(s) that
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determine the desired precedence of rows within each DISTINCT ON group.
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In order to guarantee they match, this function
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will prepend the The DISTINCT ON expressions to the ORDER BY clause.
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-}
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selectDistinctOn
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:: (SListI columns, columns ~ (col ': cols))
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=> [SortExpression outer commons grp schemas params from]
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-- ^ distinct on and return the first row in ordering
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-- ^ DISTINCT ON expression(s) and prepended to ORDER BY clause
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-> Selection outer commons grp schemas params from columns
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-- ^ selection
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-> TableExpression outer commons grp schemas params from
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