This function maintains a count, which is passed to the function as the first parameter by the aggregate, and increments it based on the result of an expression passed to the function by the second parameter. In short, you would only need such functions if you're creating your own custom aggregates.įor example, if we wanted to create an aggregate to perform conditional counts, we'd need to create a function for our aggregate to use. Note that the type of each value passed to the VARIADIC parameter has to match the function.Īggregate functions are functions used by aggregates in order to reach the result required. You could then call this function like so: SELECT create_post('My daily activity','I went to the cinema, got some lunch, caught up with friends and went to a party','cinema','movies','lunch','friends','reunion','party') VALUES (title, content, array_to_string(tags,',')) This is when you can use the VARIADIC parameter, which must always be the last parameter defined, and you define it as an array type: CREATE FUNCTION create_post(title text, content text, VARIADIC tags text) You may also have a function where you want the user to be able to specify multiple items, but you don't know how many to expect because the number can vary. CREATE FUNCTION dog_years(INOUT age int, OUT dog_years int) And INOUT, which we use to define a parameter that accepts input, but will also be included in the output.

There is also the OUT parameter, which is a way to produce an output that returns those fields in the result. This means we could use named notation, not specifying the 'active' parameter, and it would automatically set that value to 'true.' You can set the default value for a parameter if the user doesn't specify it using the DEFAULT keyword and a value of your choosing: CREATE FUNCTION create_user(username text, country text, age int, active bool DEFAULT true). UPDATE accounts SET active = false WHERE balance 50, country => 'France', username => 'Henri') But now there is a way to explicitly declare stored procedures, which also has the advantage of being able to open a new transaction, and they are now called differently too.įirstly, let's start with an example of both to get a feel of how they differ.īefore version 11, to declare a stored procedure we would just use a function with a return type of void, because we aren't looking to get any data back: CREATE FUNCTION deactivate_unpaid_accounts() RETURNS void Before PostgreSQL version 11, stored procedures were effectively functions that didn't return data. This is because the intention behind a stored procedure is to perform some sort of activity and then finish, which would then return control to the caller. In Postgres, the main functional difference between a function and a stored procedure is that a function returns a result, whereas a stored procedure does not.

SUMMARY: This article reviews the differences between stored procedures and functions in Postgres and the types of functionality they provide.

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