3.2.1.0 table.query

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table.query - Function

3.2.1 !!!PARTIAL IMPLEMENTATION!!! Make a table from a query
Description

!!!ONLY PARTIALLY IMPLEMENTED!!!.

The function tb.queryC() apprears to be a more complete implementation.

Make a table from a query applied to the current table. It is possible to specify column(s) and/or expressions to sort on and to specify the columns to be contained in the output table. See the example below. A new ”on-the-fly” table tool is returned. The new (reference) table can be given a name and will then be written to disk. Note that the resulting table is just a reference to the original table. One can make a deep copy of the query result using the copy function (see example).

Arguments


Inputs
query	Query string
	allowed:	string
	Default:	String
name	Name of resulting reference table
	allowed:	string
	Default:
sortlist	Sort string (one or more expressions separated by commas)
	allowed:	string
	Default:
columns	List of column names separated by commas
	allowed:	string
	Default:

Returns
casatable

Example

  tb.open("3C273XC1.MS")
  subt=tb.query("OBSERVATION_ID==0",
                sortlist="ARRAY_ID", columns="TIME, DATA, UVW")
  print subt.ncols()
# 23
  tb.close()
  copyt = subt.copy ("3C273XC1_spw1.MS", True)
  subt.close()
  copyt.close()

From the original table corresponding to the disk file 3C273XC1.MS, only rows with OBSERVATION_ID equal to 0 are selected and sorted by ARRAY_ID. Only the columns TIME DATA UVW are written. Thereafter a deep copy of the result is made. The table query command is equivalent to:

  SELECT TIME, DATA, UVW
  FROM 3C273XC1.MS
  WHERE OBSERVATION_ID==0
  ORDERBY ARRAY_ID

Example

The sortlist argument can be used to sort in ascending or descending order (or a mix of them) on one or more columns. Default is ascending. It is also possible to remove duplicate values using the word NODUPLICATES at the beginning.

E.g.:

  sortlist=’TIME desc’
  sortlist=’noduplicates ANTENNA1,ANTENNA2’
  sortlist=’ANTENNA1 desc, ANTENNA2 asc’
  sortlist=’desc ANTENNA1, ANTENNA2, TIME’

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