Mysql: 21 best practices for performance optimization 3 [Use LIMIT1 when there is only one row of Data]

Use LIMIT 1 when only one row of data is required

When you query a table, you know that only one result is returned, but you may need to fetch the cursor or check the number of returned records.
In this case, adding LIMIT 1 can increase performance. In this way, the MySQL database engine will stop searching after finding a piece of data, rather than continuing to query the next piece of data that matches the record.
The example below is just to find out if there are "China" users. Obviously, the latter will be more efficient than the former one. (Note that Select * is the first and Select 1 is the second)