Using the --safe-updates Option

For beginners, a useful startup option is --safe-updates (or --i-am-a-dummy, which has the same effect). It is helpful for cases when you might have issued a DELETE FROM tbl_name statement but forgotten the WHERE clause. Normally, such a statement deletes all rows from the table. With --safe-updates, you can delete rows only by specifying the key values that identify them. This helps prevent accidents.

When you use the --safe-updates option, mysql issues the following statement when it connects to the MariaDB server:

SET sql_safe_updates=1, sql_select_limit=1000, max_join_size=1000000;

See , "Server System Variables".

The SET statement has the following effects:

• You are not permitted to execute an UPDATE or DELETE statement unless you specify a key constraint in the WHERE clause or provide a LIMIT clause (or both). For example:

  UPDATE tbl_name SET not_key_column=val WHERE key_column=val;
  UPDATE tbl_name SET not_key_column=val LIMIT 1;
  

• The server limits all large SELECT results to 1,000 rows unless the statement includes a LIMIT clause.
• The server aborts multiple-table SELECT statements that probably need to examine more than 1,000,000 row combinations.

To specify limits different from 1,000 and 1,000,000, you can override the defaults by using the --select_limit and --max_join_size options:

Retornar