An automated oceanic research buoy network logs telemetry data whenever a drone or buoy makes a transmission. The record format is given in the table:
| Fieldname | Description |
|---|---|
| TransmissionTime | The time the telemetry was recorded |
| PlatformID | The unique ID of the recording platform |
| PlatformType | The type of platform – Buoy, Glider, or Submersible |
| Salinity | The salinity measurement in PSU (Practical Salinity Units) |
The log is stored in a database table called telemetry_records. The current contents of telemetry_records are shown:
| TransmissionTime | PlatformID | PlatformType | Salinity |
|---|---|---|---|
| 08:30 | BY_X1 | Buoy | 34.2 |
| 09:15 | GL_Y3 | Glider | 35.1 |
| 10:00 | SB_Z1 | Submersible | 33.8 |
| 10:45 | BY_X2 | Buoy | 35.5 |
| 11:30 | GL_Y3 | Glider | 34.9 |
| 12:15 | BY_X1 | Buoy | 36.1 |
| 13:00 | SB_Z2 | Submersible | 34.0 |
Write an SQL statement to display the platform IDs of the glider platforms that have recorded a salinity of less than 35.0.
5 exam-style questions on OCR GCSE Computer Science Additional programming techniques. Each one has a worked solution and a mark scheme showing where the marks go.