Running MySQL in ANSI mode causes it to behave in a more standard way than usual, making it easier to move to another database at a later stage. If you start MySQL with the --ansi option, the following differences apply to MySQL's behavior:
The || symbol does not mean OR; instead, it applies to string concatenation. This is the PIPES_AS_CONCAT mysqld sql-mode option.
Having spaces before function names no longer results in an error. This has the consequence that all function names become reserved words. This is the IGNORE_SPACE mysqld
sql-mode option.
REAL is a synonym for FLOAT, not for DOUBLE. This is the REAL_AS_FLOAT mysqld
sql-mode option.
The default transaction isolation level is set to SERIALIZABLE. This is the SERIALIZE mysqld sql-mode option.
The double quote (") character will be an identifier quote character, not a string quote character. This is the ANSI_QUOTES mysqld sql-mode option.