# Changes between Version 20 and Version 21 of DatabaseBasedAnalysis/table2sql

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Timestamp:
Oct 23, 2018, 6:55:08 PM (20 months ago)
Comment:

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 v20 To do the pre-deleting efficiently, it makes sense to have an INDEX created for a fast access. This can be achieved with the --index directive which adds the corresponding statement to the table creation (CREATE TABLE) == Splitting == Sometimes it is necessary to split the data into several root-trees or ascii-files, for exmple to produce a test and trainings sample. For this, two options exist --split-sequence (shortcut -S) and --split-quantile (shortcut -Q). The first defines a fixed sequence, for example -S 2 -S 1 -S 4 will write the first two events (2) to the first tree/file, the third event (1) to the second tree/file and the fourth to seventh (4) events to the third tree/file. To split even and odd events into two trees/files you have to use -S 1 -S 1. To randomly split the data use quantiles. For example, -Q 0.5 splits the data equally into two samples, -Q 0.2, -Q 0.5 -Q 0.9 splits the data into four samples of 10%, 20%, 30% and 40%. Note that splitting is defined on the rows which are received(!) from the database, i.e. before rows with NULL entries are excluded. == Debugging ==