Example
Query
SELECT * FROM stack;
Result
+------+----------+----------+
| id | username | password |
+------+----------+----------+
| 1 | admin | admin |
| 2 | stack | stack |
+------+----------+----------+
2 rows in set (0.00 sec)
You can select all columns from one table in a join by doing:
SELECT stack.* FROM stack JOIN Overflow ON stack.id = Overflow.id;
Best Practice Do not use * unless you are debugging or fetching the row(s) into associative arrays, otherwise schema changes (ADD/DROP/rearrange columns) can lead to nasty application errors. Also, if you give the list of columns you need in your result set, MySQL's query planner often can optimize the query.
Pros:
- When you add/remove columns, you don't have to make changes where you did use
SELECT * - It's shorter to write
- You also see the answers, so can
SELECT *-usage ever be justified?
Cons:
- You are returning more data than you need. Say you add a VARBINARY column that contains 200k per row. You only need this data in one place for a single record - using
SELECT *you can end up returning 2MB per 10 rows that you don't need - Explicit about what data is used
- Specifying columns means you get an error when a column is removed
- The query processor has to do some more work - figuring out what columns exist on the table (thanks @vinodadhikary)
- You can find where a column is used more easily
- You get all columns in joins if you use SELECT *
- You can't safely use ordinal referencing (though using ordinal references for columns is bad practice in itself)
- In complex queries with
TEXTfields, the query may be slowed down by less-optimal temp table processing
