Which statements are correct regarding indexes? (Choose all that apply.)
A.
When a table is dropped, the corresponding indexes are automatically dropped.
B.
For each DML operation performed, the corresponding indexes are automatically updated.
C.
Indexes should be created on columns that are frequently referenced as part of an expression.
D.
A non-deferrable PRIMARY KEY or UNIQUE KEY constraint in a table automatically creates a unique index.
Indexes allow find data fast, without reading the whole table.
Updating a table with indexes takes more time than updating a table without (because the indexes also need an update).
So you should ONLY create indexes on columns (and tables) that will ONLY be frequently in SELECT.
I choose ABD
I can see why ABD is correct. But why is C wrong?
From my understanding, if a column is frequently used as a condition then it’s better to have it indexed. What am I missing?