Which one of the following attributes must be used to optimize storage for NULL values?
Show 8.8.2 EXPLAIN Output Format The
EXPLAIN Output Columns
This section describes the output columns produced by Each output row from Table 8.1 EXPLAIN Output Columns
Note JSON properties which are
EXPLAIN Join Types The
EXPLAIN Extra Information The If you want to make your queries as fast as possible, look out for
EXPLAIN Output Interpretation You can get a good indication of how good a join is by taking the product of the values in the The following example shows how a multiple-table join can be optimized progressively based on the information provided by Suppose that you have the
For this example, make the following assumptions:
Initially, before any optimizations have been performed, the
Because One problem here is that MySQL can use indexes on columns more efficiently if they are declared as
the same type and size. In this context, To fix this disparity between
column lengths, use
Now
This is not perfect, but is much
better: The product of the A second alteration can be made to eliminate the column length mismatches for the
After that modification,
At this point, the query is optimized almost as
well as possible. The remaining problem is that, by default, MySQL assumes that values in the
With the additional index information, the join is perfect and
The It is possible in some cases to execute statements that modify data when Which function is used to handle NULL values?The SQL Coalesce and IsNull functions are used to handle NULL values. During the expression evaluation process the NULL values are replaced with the user-defined value. The SQL Coalesce function evaluates the arguments in order and always returns first non-null value from the defined argument list.
How are NULL values stored?It stores an array of bits (one per column) with the data for each row to indicate which columns are null and then leaves the data for that field blank.
Why is the value of an attribute stored as NULL?A null value in a relational database is used when the value in a column is unknown or missing.
How do you deal with NULL values in SQL?Handling SQL NULL values with Functions
ISNULL(): The ISNULL() function takes two parameters and it enables us to replace NULL values with a specified value. The expression parameter indicates the expression which we want to check NULL values.
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