| Purpose |
Executes a SQL query and returns a single value from the first row and first column. |
Executes a SQL query and returns a complete in-memory DataTable with all rows and columns. |
Executes a SQL query and returns a forward-only, read-only stream of data row by row. |
| Return Type |
Object (single value) |
DataTable (complete in-memory table). |
DbDataReader (forward-only stream). |
| Data Access |
First row, first column only. |
Any row, any column, any time. |
One row at a time, forward-only. Cannot go back to a previous row. |
| Memory Usage |
Very low. Single value only. |
High. Entire query result loaded into memory. |
Very low. Only one row in memory at a time. |
| Performance |
Fastest for single value retrieval. |
Slower for large datasets due to full in-memory copy. |
Fastest for large datasets due to streaming. |
| Best For |
Quick single value lookups. |
Flexible multi-row, multi-column queries needing post-processing. |
Large volume data reads where memory is a concern. |
| Requires Manual Close? |
No |
No |
Yes. Must be closed manually. Use Using statement to auto-close. |
| Supports Timeout? |
No |
No |
Yes. Optional .DataReaderTimeOut parameter in seconds. |
| DataTable Name |
Not applicable |
Optional. Defaults to "TableLookup". |
Not applicable. |
| Risk |
None |
Out-of-memory risk for very large datasets. |
Low. Only one row in memory at a time. |
| Supported In |
Workflows, Copy Methods, Equations. |
Workflows, Copy Methods, Equations. |
Workflows only. |