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[edit] In SELECT statements
[edit] Aliasing tables
Don't use the keyword "AS" between the table name and alias as no DBMS requires it and some don't recognize it. Instead, always write:
SELECT * FROM table t WHERE t.id = 0
[edit] Aliasing columns
Contrary to "Aliasing tables" the keyword "AS" between column name and alias is required by most database servers and should always be present:
SELECT count(*) AS cnt FROM table
[edit] Aliases for computed columns
The naming of computed columns implemented by the database servers is very different. Some name it like the computational expression ('count(*)'), most often in upper case and sometimes it isn't named at all. Therefore computed columns should be always given a name:
SELECT MAX(id) AS maxid FROM table
[edit] In other statements
Some database engines doesn't support aliases for tables in other types of statements than SELECT. Namely PostgreSQL and SQLite bail out with a SQL parsing error if aliases for tables are used in these statement types:
- INSERT
- UPDATE
- DELETE
Aliases should be avoided in them to ensure portable statements.
