Pythian Group

MySQL does not follow the ANSI SQL standard for quoting. MySQL’s default quoting behavior is that either single or double quotes can be used to quote a string (this gets me into trouble when I work with Oracle databases, as double quotes do not indicate a string!).

mysql> SELECT 'alive';
+-------+
| alive |
+-------+
| alive |
+-------+
1 row in set (0.00 sec)

mysql> SELECT "alive";
+-------+
| alive |
+-------+
| alive |
+-------+
1 row in set (0.00 sec)

Bare words are dealt with in context; in this case, a bare word would be parsed as a column name:

mysql> SELECT alive;
ERROR 1054 (42S22): Unknown column 'alive' in 'field list'

Backquotes are the way MySQL escapes table names. So, if you want a reserved word, number or operator to be the name of an object (ie, a table named “1″ or a column named “date”) you need to use backquotes to avoid a syntax error….for example:
Read the rest of this entry . . .

I was asked today about the ANSI_QUOTES SQL mode.

According to http://dev.mysql.com/doc/refman/5.0/en/server-sql-mode.html, ANSI_QUOTES mode changes the functionality of double quotes (“) to be like the backtick (`). Normally the functionality of double quotes is more like that of single quotes (‘).

You might use this when you have a table with spaces or other special characters you would like to escape, without having to use the backtick key. This is also ANSI standard SQL behavior (one of the more annoying things about Oracle is that I keep forgetting I can’t use “, only ‘).

Here is an example in the MySQL default mode — allowing ” to be more like ‘ :

mysql> use test;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
mysql> select @@SQL_MODE;
+------------+
| @@SQL_MODE |
+------------+
|            |
+------------+
1 row in set (0.00 sec)

mysql> create table `table with space` (num int);
Query OK, 0 rows affected (0.03 sec)

mysql> select * from `table with space`;
Empty set (0.00 sec)

mysql> select * from "table with space";
ERROR 1064: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '"table with space"' at line 1
mysql> select * from 'table with space';
ERROR 1064: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ''table with space'' at line 1

And here we chnage the SQL mode, and show that ” acts like ` in SQL_MODE=ANSI_QUOTES:

mysql> SET @@session.sql_mode=ANSI_QUOTES;
Query OK, 0 rows affected (0.00 sec)

mysql> select @@SQL_MODE;
+-------------+
| @@SQL_MODE  |
+-------------+
| ANSI_QUOTES |
+-------------+
1 row in set (0.00 sec)

mysql> select * from `table with space`;
Empty set (0.00 sec)

mysql> select * from "table with space";
Empty set (0.00 sec)

mysql> select * from 'table with space';
ERROR 1064: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ''table with space'' at line 1

mysql>

If you’re wondering why all your queries are giving strange results such as what we saw above, or even ERROR 1054: Unknown column 'col_name' in 'field list' if what you are quoting is a string that MySQL is interpreting as a column name, check your SQL mode.