DNA Sequence String Manipulation | Dataford Interview Questions

Explain how you would handle string manipulation tasks involving DNA sequences using SQL and/or Python.

Using the provided tables, write a PostgreSQL query that returns valid DNA sequences after trimming and uppercasing the input. Exclude null, empty, invalid, short, and unmatched records.

Output

One row per valid sequence with sample_label, sequence_id, normalized_sequence, sequence_length, gc_count, and reverse_complement
Include sequences containing only A, C, G, and T with at least 6 bases
Sort by sample_label, then sequence_id

Schema

dna_sequences

Column	Type	Description
sequence_idPK	INT	Unique identifier for the DNA sequence
sample_id	INT	References the DNA sample
sequence_text	TEXT	Raw DNA sequence text

dna_samples

Column	Type	Description
sample_idPK	INT	Unique identifier for the sample
sample_label	VARCHAR(100)	Human-readable sample label

Your question is DNA Sequence String Manipulation. Start with the requirements and the two tables in the Question tab.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.

Problem