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8.5.4.2 Using the `--safe-updates' Option
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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 MySQL server:
SET SQL_SAFE_UPDATES=1,SQL_SELECT_LIMIT=1000, SQL_MAX_JOIN_SIZE=1000000;
See set-option.
The `SET' statement has the following effects:
* You are not allowed 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:
shell> mysql --safe-updates --select_limit=500 --max_join_size=10000
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