Helper Functions

When writing custom APIs, the following helper functions are available in the DAPs to retrieve data.

Data model

Unlike a typical kdb+ database, table data is not stored in the base table name. Data may be distributed across an on-disk table and multiple in-memory tables (see Late data). It is highly recommended to use the following helper functions.

.kxi.selectTable

This a general-purpose function to retrieve data for a specified table. It creates a single synthesized view of the table, removing the requirement for you to know exactly how the data is distributed across multiple internal tables. This is the recommended method for accessing data.

• Parameters

  • tn - symbol - Table name.
  • ts - timestamp[2] - Start and end time (inclusive) of the data to select. This may be an empty list for reference tables.
  • wc - list - Functional where clause.
  • bc - dict/boolean - Functional by clause.
  • cn - symbol[] - Full list of columns to select. This MUST include all columns needed in agg.
  • agg - dict - Functional agg clause.

• Return

  • table - Result of select.

Examples

.kxi.selectTable[`trade;2024.04.10D 2024.04.15D;((=;`sym;enlist`AAPL);(>;`price;100));enlist[`sym]!enlist`sym;`price`size;`price`size!((avg;`price);(max;`size))] / Complex select on timeseries data
.kxi.selectTable[`referenceTable;();();0b;`x`y`z;()] / Simple select on reference data

Advanced

.kxi.selectTable is the recommended way to retrieve data. However, you may wish to access internal tables individually for greater control. It is not recommended to use these functions without deep knowledge of the data model used in kdb Insights, refer to Late data for more information.

.da.getTableMem

Retrieves the portion of the table held in memory.

• Parameters

  • tn - symbol - Table name.

• Return

  • table - In-memory portion of the table.

Example

q).da.getTableMem`myTable
x y
---
1 3
2 4

.da.getTableDelta

Retrieves the portion of the table held in the in-memory delta table.

• Parameters

  • tn - symbol - Table name.

• Return

  • table - Delta portion of the table.

  Example

  q).da.getTableDelta`myTable
  x y
  ---
  1 3
  2 4