Select values

TL;DR; aka Too long didn't read
Select and filter
All options
Result details
Performance
From shell

TL; DR;

Fastest way to select values in 3 lines:

# import RCDB
from rcdb.provider import RCDBProvider

# connect to DB
db = RCDBProvider("mysql://rcdb@hallddb.jlab.org/rcdb")

# select values with query
table = db.select_values(['polarization_angle','beam_current'], "@is_production", run_min=30000, run_max=30050)

table will contain 3 columns run_number, polarization_angle, beam_current. Like:

[[30044,  -1.0,  UNKNOWN],
 [30045,  45.0,  PARA   ],
...]

Select and filter

The fastest designed way to get values from RCDB is by using select_values function. The full example is here: $RCDB_HOME/python/example_select_values.py

The simplest usage is to put condition names and a run range:

from rcdb.provider import RCDBProvider

db = RCDBProvider("mysql://rcdb@hallddb.jlab.org/rcdb")

table = db.select_values(['polarization_angle','polarization_direction'], run_min=30000, run_max=30050)

# Print results
print(" run_number, polarization_angle, polarization_direction")
for row in table:
    print row[0], row[1], row[2]

output:

30044 -1.0 UNKNOWN
30045 45.0 PARA

By default, the result is a table with runs numbers in the first column and requested conditions values in other columns.

Filter

It is possible to put a selection query as a second argument as in the above example:

table = db.select_values(['polarization_angle'], "@is_production", run_min=30000, run_max=30050)

Exact run numbers

Instead of using run range one can specify exact run numbers using runs argument

table = db.select_values(['event_count'], "@is_production", runs=[30300,30298,30286])

All options

                                                                             # Default value | Descrition
                                                                             #---------------+------------------------------------
table = db.select_values(val_names=['event_count'],                          # []            | List of conditions names to select, empty by default
                          search_str="@is_production and event_count>1000",  # ""            | Search pattern.
                          run_min=30200,                                     # 0             | minimum run to search/select
                          run_max=30301,                                     # sys.maxsize   | maximum run to search/select
                          sort_desc=True,                                    # False         | if True result runs will by sorted descendant by run_number, ascendant if False
                          insert_run_number=True,                            # True          | If True the first column of the result will be a run number
                          runs=None)                                         # None          | a list of runs to search from. In this case run_min and run_max are not used

Remarks:

val_names. If val_names list is empty, run numbers will be selected (assuming that insert_run_number=True by default)
search_str. If ```search_str`` is empty, the function doesn't apply filters and just select values for all runs according to ['run_min' - 'run_max'] or 'runs' list

Result details

The result of select_values (called table in the examples) holds more information than just values. Here some useful fields:

table.selected_conditions - selected condition names (or call it column titles)
table.performance['total'] - function execution time

table = db.select_values(['beam_current'], "@is_production", runs=[30300,30298,30286])
print("We selected: " + ", ".join(table.selected_conditions))
print("It took {:.2f} sec ".format(table.performance['total']))

result:

We selected: run, beam_current
It took 0.14 sec

Performance

calling select_values is the fastest way to get such tables of values. Before RCDB had a chain of functions select_runs(...).get_values(...) to select values. This chain is still there but it is much slower. MUCH SLOWER.

More info about select runs && get values

Select runs & get values (python)

From shell

(Shell one liner)

Suppose one wants to select values in a bash script but doesn't want to create a separate python script. It is possible to call python -c "semicolon;separated;commands"

Combining everything in such one-liner:

python -c "import rcdb.provider;t=rcdb.provider.RCDBProvider('mysql://rcdb@hallddb.jlab.org/rcdb').select_values(['polarization_angle','polarization_direction'], run_min=30000, run_max=31000);print('\n'.join([' '.join(map(str, r)) for r in t]))"

Shouldn't be there an easier way? It was planned to have rcdb sel command doing it. But it hasn't been fully implemented yet. If you have a spare time (or student) to contribute, please, contact me (Dmitry)