append mysql text to select from?

My old answer only goes to PostgresSQL, I did not read your question properly sorry. In MySQL you use the CONCAT function:

SELECT id, CONCAT(feld1, ' Liter')
FROM tabelle;

— Original answer —

If I understand it correctly, you want an issue like

| ID | Anzahl   |
|----|----------|
|  1 | 10 Liter |
|  2 | 20 Liter |

You can use a concatenation operator in the issue. That’s what it looks like.

SELECT id, feld1 || ' Liter'
FROM tabelle;