================================================================================
basic
================================================================================
do $$ begin
if true then select 1; end if;
end $$;
--------------------------------------------------------------------------------

(source_file
  (do_block
    (block
      (dollar_quote)
      (body
        (if_statement
          (true)
          (select_statement
            (select_item
              (number)))))
      (dollar_quote))))

================================================================================
many statements
================================================================================
do $$ begin
if true then select 1; select 2; end if;
end $$;
--------------------------------------------------------------------------------

(source_file
  (do_block
    (block
      (dollar_quote)
      (body
        (if_statement
          (true)
          (select_statement
            (select_item
              (number)))
          (select_statement
            (select_item
              (number)))))
      (dollar_quote))))

================================================================================
if then else
================================================================================
do $$ begin
if var <> 5 then return 1; else return 2; end if;
end $$;
--------------------------------------------------------------------------------

(source_file
  (do_block
    (block
      (dollar_quote)
      (body
        (if_statement
          (op_expression
            (identifier)
            (comparison_op)
            (number))
          (return_statement
            (number))
          (return_statement
            (number))))
      (dollar_quote))))

================================================================================
if then else if
================================================================================
do $$ begin
if var > 5 then return 1; elsif var = 4 then return 2; end if;
end $$;
--------------------------------------------------------------------------------

(source_file
  (do_block
    (block
      (dollar_quote)
      (body
        (if_statement
          (op_expression
            (identifier)
            (comparison_op)
            (number))
          (return_statement
            (number))
          (op_expression
            (identifier)
            (comparison_op)
            (number))
          (return_statement
            (number))))
      (dollar_quote))))

================================================================================
elseif/elsif
================================================================================
do $$ begin
if var > 5 then return 1; elsif var = 4 then return 2; elseif var = 3 then return 3; else return 4; end if;
end $$;
--------------------------------------------------------------------------------

(source_file
  (do_block
    (block
      (dollar_quote)
      (body
        (if_statement
          (op_expression
            (identifier)
            (comparison_op)
            (number))
          (return_statement
            (number))
          (op_expression
            (identifier)
            (comparison_op)
            (number))
          (return_statement
            (number))
          (op_expression
            (identifier)
            (comparison_op)
            (number))
          (return_statement
            (number))
          (return_statement
            (number))))
      (dollar_quote))))

================================================================================
nested
================================================================================
do $$ begin
if true then return 1; else if var = 4 then return 2; end if; end if;
end $$;
--------------------------------------------------------------------------------

(source_file
  (do_block
    (block
      (dollar_quote)
      (body
        (if_statement
          (true)
          (return_statement
            (number))
          (if_statement
            (op_expression
              (identifier)
              (comparison_op)
              (number))
            (return_statement
              (number)))))
      (dollar_quote))))

================================================================================
if is not null
================================================================================
do $$ begin
if foo is not null then select 1; end if;
end $$;
--------------------------------------------------------------------------------

(source_file
  (do_block
    (block
      (dollar_quote)
      (body
        (if_statement
          (op_expression
            (identifier)
            (comparison_null))
          (select_statement
            (select_item
              (number)))))
      (dollar_quote))))

================================================================================
if is not distinct from
================================================================================
do $$ begin
if foo is not distinct from bar then select 1; end if;
end $$;
--------------------------------------------------------------------------------

(source_file
  (do_block
    (block
      (dollar_quote)
      (body
        (if_statement
          (op_expression
            (identifier)
            (comparison_kw)
            (identifier))
          (select_statement
            (select_item
              (number)))))
      (dollar_quote))))

================================================================================
if is distinct from
================================================================================
do $$ begin
if foo is distinct from bar then select 1; end if;
end $$;
--------------------------------------------------------------------------------

(source_file
  (do_block
    (block
      (dollar_quote)
      (body
        (if_statement
          (op_expression
            (identifier)
            (comparison_kw)
            (identifier))
          (select_statement
            (select_item
              (number)))))
      (dollar_quote))))