9.5. Treatment of Reserved Words in MySQL

A common problem stems from trying to use an identifier such as a table or column name that is a reserved word such as SELECT or the name of a built-in MySQL data type or function such as TIMESTAMP or GROUP.

If an identifier is a reserved word, you must quote it as described in Section 9.2, “Database, Table, Index, Column, and Alias Names”. Exception: A word that follows a period in a qualified name must be an identifier, so it is not necessary to quote it, even if it is a reserved word.

You are permitted to use function names as identifiers. For example, ABS is acceptable as a column name. However, by default, no whitespace is allowed in function invocations between the function name and the following ‘(’ character. This requirement allows a function call to be distinguished from a reference to a column name.

A side effect of this behavior is that omitting a space in some contexts causes an identifier to be interpreted as a function name. For example, this statement is legal:

mysql> CREATE TABLE abs (val INT);

But omitting the space after abs causes a syntax error because the statement then appears to invoke the ABS() function:

mysql> CREATE TABLE abs(val INT);
ERROR 1064 (42000) at line 2: You have an error in your SQL
syntax ... near 'abs(val INT)'

If the IGNORE_SPACE SQL mode is enabled, the server allows function invocations to have whitespace between a function name and the following ‘(’ character. This causes function names to be treated as reserved words. As a result, identifiers that are the same as function names must be quoted as described in Section 9.2, “Database, Table, Index, Column, and Alias Names”. The server SQL mode is controlled as described in Section 5.2.5, “The Server SQL Mode”.

The words in the following table are explicitly reserved in MySQL 5.0. At some point, you might update to a higher version, so it's a good idea to have a look at future reserved words, too. You can find these in the manuals that cover higher versions of MySQL. Most of the words in the table are forbidden by standard SQL as column or table names (for example, GROUP). A few are reserved because MySQL needs them and (currently) uses a yacc parser. A reserved word can be used as an identifier if you quote it.

The following are new reserved words in MySQL 5.0: ASENSITIVE, CALL, CONDITION, CONNECTION, CONTINUE, CURSOR, DECLARE, DETERMINISTIC, EACH, ELSEIF, EXIT, FETCH, GOTO, INOUT, INSENSITIVE, ITERATE, LABEL, LEAVE, LOOP, MODIFIES, OUT, READS, RELEASE, REPEAT, RETURN, SCHEMA, SCHEMAS, SENSITIVE, SPECIFIC, SQL, SQLEXCEPTION, SQLSTATE, SQLWARNING, TRIGGER, UNDO, UPGRADE, WHILE.

MySQL allows some keywords to be used as unquoted identifiers because many people previously used them. Examples are those in the following list: