A_SYB_USE_DROPDOWN_QUERIES configuration variable

Setting A_SYB_USE_DROPDOWN_QUERIES to a nonzero value causes select queries sent to the database to be of the drop-down variety, instead of a single large query. This variable is accessed only during a positioning operation, so you can set it at different times for different tables. For example, if you have a file with three fields in the primary key (keyseg1, keyseg2, keyseg3), and your COBOL program performs a START, the following query is sent to the database:

select (columns) from (table) where 
((keyseg1 = value1 and keyseg2 = value2 and 
keyseg3 > value3) or (keyseg1 = value1 and 
keyseg2 > value2) or (keyseg1 > value1)) 
order by keyseg1, keyseg2, keyseg3

If you use drop-down queries, the following collection of queries is sent instead:

select (columns) from (table) where (keyseg1
= value1 and keyseg2 = value2 and keyseg3 >
value3) order by keyseg1, keyseg2, keyseg3

When that set is finished, the interface sends:

select (columns) from (table) where (keyseg1 
= value1 and keyseg2 > value2) order by 
keyseg1, keyseg2, keyseg3

And when that set is finished, the interface sends:

select (columns) from (table) where (keyseg1
> value1) order by keyseg1, keyseg2, keyseg3

There are advantages and disadvantages to each method. If you use the A4GL_WHERE_CONSTRAINT variable, you should probably set A_SYB_USE_DROPDOWN_QUERIES to 0, because the WHERE constraint limits the result set sufficiently that the larger query will be more efficient. See The WHERE Constraint for additional information.

If you usually START files and read to the end, you should set A_SYB_USE_DROPDOWN_QUERIES to 0, because a fewer number of queries need to be sent to the database. On the other hand, if you START files and stop reading after some condition, but haven’t used the WHERE constraint, then you may get more efficient access by setting this variable to 1 and using the drop-down style of query. In either case, we recommend that you run some tests to see which value of this variable makes the most sense for your application. While the default value is 0 (OFF, FALSE, NO), this configuration variable can also take the value of ON (TRUE, YES).

A_SYB_USE_DROPDOWN_QUERIES number