Several scenarios for MySQL failure

1, if there is an or in the query condition, even if the condition of the query with an index will be invalidated, if you want to use or, and do not want to invalidate the index, you can only add all the columns in the OR condition index

2, like query one of the beginning is not indexed,

3. Implicit conversion will invalidate the index

For example, if the field type is varchar and indexed, but a numeric type is passed, the index is invalidated, and if the field type is int, the value is varchar, but does not affect the index

4, the query condition using the function on the index list, or on the index column using the-+ operator, will also be invalidated

5, to be continued ....

Several scenarios for MySQL failure