Remove Histogram_*::is_available(), it is not applicable anymore.
Fix compilation on Windows

Factor the code that updates count, count_distinct,
count_distinct_single_occurrence into class Basic_stats_collector

Change from Histogram_builder and its descendant Histogram_builder_json
to  Histogram_builder (the interface), and Histogram_binary_builder,
Histogram_json_builder.

In Histogram_json_builder, do not forget to collect the right bound
of the right-most bucket.

There are "local" histograms that are allocated by one thread for
one TABLE object, and "global" that are allocated for TABLE_SHARE.

- Don't use 'res' uninitialized
- multiply it by col_non_nulls before set_if_bigger(...) call.

Signed-off-by: Michael Okoko <okokomichaels@outlook.com>

Signed-off-by: Michael Okoko <okokomichaels@outlook.com>

Signed-off-by: Michael Okoko <okokomichaels@outlook.com>

* Also merges tests relating to JSON statistics into one file
Signed-off-by: Michael Okoko <okokomichaels@outlook.com>

Signed-off-by: Michael Okoko <okokomichaels@outlook.com>

Signed-off-by: Michael Okoko <okokomichaels@outlook.com>

Signed-off-by: Michael Okoko <okokomichaels@outlook.com>

Signed-off-by: Michael Okoko <okokomichaels@outlook.com>

* it also adds an "explain select" statement to the test so that the fprintf calls
  can print the computed intervals to mysqld.1.err
Signed-off-by: Michael Okoko <okokomichaels@outlook.com>

Signed-off-by: Michael Okoko <okokomichaels@outlook.com>

This fixes the wrong calculation for avg_frequency in json histograms
by replacing the specific histogram objects with the generic Histogram_base class.

It also restores get/set size functions as they were useful in calculating fields
for binary histogram.
Signed-off-by: Michael Okoko <okokomichaels@outlook.com>

A demo of how to use in-memory data structure for histogram.
The patch shows how to
* convert string form of data to binary form
* compare two values in binary form
* compute a fraction for val in [X, Y] range.

grep for GSOC-TODO for notes.

Signed-off-by: Michael Okoko <okokomichaels@outlook.com>

Signed-off-by: Michael Okoko <okokomichaels@outlook.com>