When is DECLARE absolutely required?
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After the CREATE PROCEDURE line, the next line defines a parameter variable. Why isn't the DECLARE keyword used here? Starting on line 5, when other variables are declared, the keyword DECLARE is used.
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That's how input parameters are declared. That's just how T-SQL works.
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DECLARE is for creating local variables. These are different from parameters. Both start with @, but are treated differently within the engine, therefore different mechanisms for definition.
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They may look the same, but there are more differences than just leaving out the word DECLARE.
Parameter declarations can have the attributes OUTPUT, READONLY, and VARYING; local variables cannot.
A variable declaration with a value (@p1 INT = 123 ) will always initialize the variable to that value. For a parameter, that syntax is a default value and makes the parameter optional. The value in the parameter declaration is only used if the parameter is omitted from the EXEC statement.
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