PostgreSQL for MySQL Users: Unterschied zwischen den Versionen

Version vom 13. September 2011, 20:07 Uhr

Siehe auch:

• PostgreSQL

Licensing:

• MySQL: Dual Licensed
• PostgreSQL: BSD-Style

MySQL's INSERT UPDATE

Option 1) Write a function like:

 create function doinsert(_id integer, _value text) returns void as $$
 begin
  update thetable set value = _value where id = _id;
  if not found then
     insert into thetable(id, value) values (_id, _value);
   end if
 end;
 $$ language plpgsql;

Option 2) Use two SQL statements:

 -- update the existing
 update realTable set value = (select value from tmp where tmp.id = realTable.id)
 where exists (select value from tmp where tmp.id = realTable.id);
 -- insert the missing
 insert into realTable(id, value)
 select id, value from tmp where not exists(select 1 from realTable where tmp.id = realTable.id);

MySQL's AUTO INCREMENT

• MySQL: id INT UNSIGNED NOT NULL AUTO_INCREMENT
• PostgreSQL: id SERIAL
• Siehe auch 1 und 2

MySQL's DROP TABLE IF EXIST

• Existiert auch in PostgreSQL ab Version 8.2
• Bei früheren Versionen gibt es einen Workaround:
  •  % select count(*) from pg_class where relname = 'mytable'
  • return 1 if mytable exists, and 0 if it doesn't
  • so you can run a DROP TABLE command (or not) based on the returned value.

MySQL's INT UNSIGNED (Cardinal)

• MySQL: column INT UNSIGNED
• PostgreSQL: column INT CHECK (column > 0)

MySQL's Index-Typ

• MySQL: INDEX idx_id(id)
• PostgreSQL: CREATE INDEX idx_id ON TABLENAME(id);

MySQL's Query Resultset Limit

• MySQL: SELECT * FROM tbl LIMIT 10, 5
• PostgreSQL: SELECT * FROM tbl LIMIT 5 OFFSET 10

Data types of MySQL versus PostgreSQL