Section table
(1) Horizontal segmentation: Raise the query speed, but the application will be complicated because the application should be combined with multiple tables;
(2) Vertical segmentation: Use a list of fields with high access frequencies, in the case where the columns in different segmentation tables are small in the case where they are queried or updated.
2. Keep redundant columns: When two or more tables often need to be connected, you can add a number of redundant columns on one of the tables to avoid the connection between the surface is too frequent. Generally, in the case where the data of redundant columns is not changed frequently.
3. Increase the registration column: Derived columns are calculated by many other column calculations in the table, and increase the registration column to reduce statistical operations, greatly shorten the calculation time during the data summary.
4. INULL and ISNOTNULL: Indexes cannot be used on columns with NULL values.
5. Connection column: For columns with connections, the optimizer does not use index even if the last connection value is a static value.
6. LIKE statement of bandpass: The wildcards appearing in the word cannot use the index.
7.Orderby statement: Any non-index item on the ORDERBY statement will reduce the query speed.
8. Try to score <> to split> and <.
9.IN and EXISTS: IN To traverse all records, Exists only traversed the requirements of the eligible record, so the EXISTS is efficient.
