PostgreSQL的if判断语句

PostgreSQL if判断语句
1、语法：
if condition then
    statement;
end if;

案例1：
do $$
declare 
    a integer := 10;
    b integer := 20;
begin 
    if a>b then 
        raise notice 'a is greater then b';
    end if;
    
    if a<b then 
        raise notice 'a is less then b';
    end if;
    
    if a=b then
        raise notice 'a is equal to b ';
    end if;
end; $$



2、语法：
if then else
if condition then
    statement1;
else
    statement2;
end if;

案例：
do $$
declare 
    a integer :=10;
    b integer :=20;
begin 
    if a > b then 
        raise notice 'a is greater then b';
    else 
        raise notice 'a is not greater then b';
    end if;

end; $$



3、语法：
if condition then 
    statement1;
elsif condition then 
    statement2;
    ...
else
    statementn;
end if;

案例：
do $$
declare
    a integer :=20;
    b integer :=20;
begin
    if a > b then 
        raise notice 'a is greater then b';
    elsif a = b then 
        raise notice 'a is equal to b';
    elsif a < b then
        raise notice 'a is less then b';
    else
        raise notice 'error';
    end if;
end; $$