latestKeyedTable

Syntax

latestKeyedTable(keyColumns, timeColumn, [X1], [X2], …..)

or

latestKeyedTable(keyColumns, timeColumn, capacity:size, colNames, colTypes)

or

latestKeyedTable(keyColumns, timeColumn, table)

Arguments

Added parameter timeColumn for the function keyedTable.

timeColumn is a string indicating the column name of the time column. The time column can be integral or temporal type.

Details

Create a keyed table, which is a special type of in-memory table with primary key. The primary key can be one column or multiple columns. Compared to the keyedTable, latestKeyedTable adds a time column to determine whether to update records.

When a new record is appended to the keyed table, if its timestamp is smaller than that of the existing row which has the same primary key, it does not overwrite the existing row. latestKeyedTable deduplicates records with the same primary key based on the time column, which affects its writing performance (relatively slow compared with keyedTable).

Note:

The primary key cannot be modified (with functions update, or replaceColumn!) or deleted (with functions alter, or dropColumns!).
The function cannot be used to create a table containing array vectors.

Refer to keyedTable for the optimization of query performance on latestKeyedTable.

Examples

Example 1. Create a keyed table.

Scenario 1:

$ sym=`A`B`C`D`E
$ id=5 4 3 2 1
$ val=52 64 25 48 71
$ timeCol = 2022.12.07T00:00:00.001+0..4
$ t=latestKeyedTable(`sym`id,`timeCol,sym,id,timeCol,val)
$ t;

sym	id	timeCol	val
A	5	2022.12.07T00:00:00.001	52
B	4	2022.12.07T00:00:00.002	64
C	3	2022.12.07T00:00:00.003	25
D	2	2022.12.07T00:00:00.004	48
E	1	2022.12.07T00:00:00.005	71

Scenario 2:

$ t=latestKeyedTable(`sym`id,1:0,`sym`id`val,[SYMBOL,INT,INT])
$ insert into t values(`A`B`C`D`E,5 4 3 2 1,2022.12.07T00:00:00.001+0..4,52 64 25 48 71);

Scenario 3:

$ tmp=table(sym, id, timeCol, val)
$t=latestKeyedTable(`sym`id, `timeCol, tmp);

Example 2. Update a keyed table.

If the new row has the same primary key value as an existing row, whether to update the record is determined by the time column.

$ insert into t values(`A`A`E,5 5 1, 2022.12.07T00:00:00.001 2022.12.07T00:00:00.007 2022.12.07T00:00:00.003, 44 66 28);
$ t;

sym	id	timeCol	val
A	5	2022.12.07T00:00:00.007	66
B	4	2022.12.07T00:00:00.002	64
C	3	2022.12.07T00:00:00.003	25
D	2	2022.12.07T00:00:00.004	48
E	1	2022.12.07T00:00:00.005	71

Related functions: keyedTable, indexedTable, latestIndexedTable