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SQL: coalesce

The expression coalesce(p1, p2, … pₙ) evaluates to the first parameter (pₓ) that is not null.

Recursive definition of coalesce

The SQL expression coalesce can be defined recursively:

coalesce(p₁, p₂) is equivalent to the following case expression:

case
   when p1 is not null then p1
   else                     p2
end

coalesce(p₁, p₂, … pₙ) is equivalent to

case
   when p1 is not null then p1
   else coalesce(p₂, … pₙ)
end

Index

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