08-create-variables-and-blocks-with-do-declare.md

Create Variables and Blocks with Do / Declare

How Do/Declare Works

We use do to define an anonymous code block. Follow these steps to create a do block.

1. Start with do. This is kind of like the function keyword in JavaScript.

2. We have to include the $$ which act like curly braces in JavaScript.

3. Type declare. This initiates the declaration section of the block where variables are declared.

4. Now declare your variable name followed by the variable type. We assign value to the variable using := and set it equal to whatever value we want. End the statement with a ;

5. Type begin. All statements after the begin command will be executed.

6. Include the command you would like to be executed.

7. End your statement with end $$ and don't forget your ;.

do $$
declare
handle uuid := '29587e31-b631-4b2a-a31f-9771a43db98a';
begin
insert into members values (now(), null, handle, 'Stacy', 'stacy@gmail.com)
end $$
;

Do/Declare with if

We can add an if clause into a do/declare block

do $$
declare
handle uuid := '29587e31-b631-4b2a-a31f-9771a43db98a';
startDate date;

begin
select start_date into startDate from members where user_handle = handle;
if (startDate is not null) then
insert into members values (startDate, null, uuid_generate_v4(), 'Melissa', 'melissa@gmail.com');
end if;
end $$;

Using Built-in Funtions When Declaring Variables

We can use built-in functions with our variables. Here's an example.

do $$
declare
    handle uuid := '29587e31-b631-4b2a-a31f-9771a43db98a';
    someDate date := '2019-04-01';
    createDate date := least('2019-01-12', someDate);

In this example, the least function is used.