4 points to be aware of in optimizing SQL statements

1. Try not to perform functional processing of column names. Instead, it is processed for the following values

For example, where col1 =-5 efficiency is higher than where-col1=5 efficiency

The column values are evaluated because of the subsequent conditions. The optimizer cannot use the index under such conditions

Instead, you have to evaluate all the values before you can compare them.

2. Try to use the same value as the play column to operate

If col1 is a numeric type

So for example where col1 = 2 and where col1= ' 2′

The former is more efficient

Because when comparing characters and numeric types,

The engine needs to convert both to double and then compare.

3. Reduce the use of functions

For example where col1 >= ' 2009-10-26′and col1 <= ' 2009-10-27′

And where DateDiff (Day,col1,getdate ()) =0

The latter is used for function processing. So the index on the col1 can't be used anymore.

4. Try not to use or

General conditions for OR

The optimizer typically uses full table scans