
Explanation

Box 1: UPDATE STATISTICS
Box 2: SAMPLE 20 PERCENT
UPDATE STATISTICS tablenameSAMPLE number { PERCENT | ROWS }
Specifies the approximate percentage or number of rows in the table or indexed view for the query optimizer to use when it updates statistics. For PERCENT, number can be from 0 through 100 and for ROWS, number can be from0 to the total number of rows.
Box 3: UPDATE STATISTICS
Box 4: WITH FULLSCAN
FULLSCAN computes statistics by scanning all rows in the table or indexed view. FULLSCAN and SAMPLE
100 PERCENT have the same results. FULLSCAN cannot be used with the SAMPLE option.
References: https://msdn.microsoft.com/en-us/library/ms187348.aspx