Quotation Mark "

The SQL:1999 standard specifies that double quote (“) (QUOTATION MARK) is used to delimit identifiers.

<delimited identifier> ::= <double quote> <delimited identifier body> <double quote>

Oracle, PostgreSQL, MySQL, MSSQL and SQlite all support " as the identifier delimiter.

They don’t all use " as the ‘default’. For example, you have to be running MySQL in ANSI mode and SQL Server only supports it when QUOTED_IDENTIFIER is ON.