cs .select()
Description:
Attach the record filtering action to a cursor and return the original cursor.
Syntax:
cs.select(x)
Note:
The function attaches a computation to cursor cs, which will calculate expression x against each of the records in cursor cs and get records that make value of x true, and return the original cursor cs.
When parameter x is omitted, get all records of cursor cs. The function supports multicursors.
This is a delayed function.
Option:
|
@c |
Enable getting the eligible member(s) beginning from the first member that makes Boolean expression x true from left to right until the first ineligible member that makes Boolean expression x false appears. |
|
@v |
Use column-wise computation when parameter cs is a column-wise cursor and also return a column-wise cursor. |
Parameter:
|
cs |
A cursor |
|
x |
A Boolean value |
Return value:
Cursor
Example:
|
|
A |
|
|
1 |
=demo.cursor("select * from SCORES") |
Return a cursor:
|
|
2 |
=A1.select(STUDENTID>10) |
Attach a computation to cursor A1, which will select records where STUDENTID is greater than 10 from the cursor, and return cursor A1:
|
|
3 |
=A1.fetch() |
Fetch data from cursor A1 where A2’s computation is executed (it would be better that data is fetched in batches when a large amount of data is involved):
|
When using @v option:
|
|
A |
|
|
1 |
=connect("demo").cursor@v("select * from employee") |
Return a column-wise cursor. |
|
2 |
=A1.select@v(DEPT=="HR") |
Perform column-wise computation. |
When using @c option:
|
|
A |
|
|
1 |
=[4,8,10,3,5,7,9,11,13,7].cursor() |
|
|
2 |
=A1.select@c(~>7) |
@c option enables to get members from the first member greater than 7 until the first member less than 7 appears. |
|
3 |
=A2.fetch() |
Result: [8,10]. |