I wonder if it's a problem, if a table or column name contains upper case letters. Something lets me believe databases have less trouble when everything is kept lower case. Is that true? Which databases don't like any upper case symbol in table and column names?
I need to know, because my framework auto-generates the relational model from an ER-model.
(this question is not about whether it's good or bad style, but only about if it's a technical problem for any database)
It is not a technical problem for the database to have uppercase letters in your table or column names, for any DB engine that I'm aware of. Keep in mind many DB implementations use case sensitive names, so always refer to tables and columns using the same case with which they were created (I am speaking very generally since you didn't specify a particular implementation).
For MySQL, here is some interesting information about how it handles identifier case. There are some options you can set to determine how they are stored internally. http://dev.mysql.com/doc/refman/5.0/en/identifier-case-sensitivity.html
The SQL-92 standard specifies that identifiers and keywords are case-insensitive (per A Guide to the SQL Standard 4th edition, Date / Darwen)
That's not to say that a particular DBMS isn't either (1) broken, or (2) configurable (and broken)
From a programming style perspective, I suggest using different cases for keywords and identifiers. Personally, I like uppercase identifiers and lowercase keywords, because it highlights the data that you're manipulating.
As far as I know for a common L.A.M.P. setup it won't really matter - but be aware that MySQL hosted on Linux is case sensitive!
To keep my code tidy I usually stick to lower case names for tables and colums, uppercase MySQL-Code and mixed Upper-Lower-Case variables - like this:
SELECT * FROM my_table WHERE id = '$myNewID'
As far as I know there is no problem using either uppercase and lowercase. One reason for the using lower case convention is so that queries are more readable with lowercase table and column names and upper case sql keywords:
SELECT column_a, column_b FROM table_name WHERE column_a = 'test'
If you're using postgresql and PHP, for instance, you'd have to write your query like this:
$sql = "SELECT somecolumn FROM \"MyMixedCaseTable\" where somerow= '$somevar'";
"Quoting an identifier also makes it case-sensitive, whereas unquoted names are always folded to lower case. For example, the identifiers FOO, foo, and "foo" are considered the same by PostgreSQL, but "Foo" and "FOO" are different from these three and each other. (The folding of unquoted names to lower case in PostgreSQL is incompatible with the SQL standard, which says that unquoted names should be folded to upper case. Thus, foo should be equivalent to "FOO" not "foo" according to the standard. If you want to write portable applications you are advised to always quote a particular name or never quote it.)" http://www.postgresql.org/docs/8.4/static/sql-syntax-lexical.html#SQL-SYNTAX-IDENTIFIERS
So, sometimes, it depends on what you are doing...