PostgreSQL for MySQL Users
Siehe auch:
Licensing:
- MySQL: Dual Licensed
- PostgreSQL: BSD-Style
Inhaltsverzeichnis
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'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 Unsigned integer (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
| Mysql | | PostgreSQL | | | Typ | Beschreibung | Typ | Beschreibung | | tinyint | -128 ... 127 | | | | smallint | -32768 ... +32767 | int2 | -32767 ... +32768 | | int | -2147483648 ... +2147483647 | int4 | -2147483648 ... +2147483647 | | | | int8 | +/- 18 Dezimalstellen | | float(n) | n E {4;8}, Einf./doppelte Genauig.| float4 | 6 Dez.Stellen| | | | float8 | 15 Dezimalstellen | | date | YYYY-MM-DD Datumsformat | date | Datum, Datumformate mit SET DATESTYLE=Value einstellbar | | time | HH-MM-SS Zeitformat | time | Uhrzeit, Auflösung 1 Mikrosekunde | | char(m) | Zeichenkette mit fester Länge | char | ein Zeichen | | varchar(m) | variable Länge, max. m Zeichen | varchar(n) | 4+n Bytes | | blob | Binary Large Object, wird für Texte gebraucht, "TINY", "", "LONG" | bytea | | | | | money | 4 Byte, -21474836,48 ... +21474836,47 | | | | text | Variable Länge| | | | bool | Kann den Wert 't' oder 'f' annehmen |