SQL

Social Network Relationship Graph | SQL Use Case

Here is SQL test I took during a job interview. First is the description, or you can skip directly to the answer. Description: A social network under development needs a query that returns all profiles and the types of their relationships with each other. The result should have the following columns: profile | %related_profile_1% .. %related_profile_N% - type of relation of specific profiles: The column name is the related profile username....

Dialer Application Weekly Call Stats | SQL Use Case

Here is SQL test I took during a job interview. First is the description, or you can skip directly to the answer. Description: As part of developing the call history functionality of a dialer application, create a query that returns a list of all contacts, the total duration of their calls, and the number of calls during the work week and weekends. The result should have the following column: full_name | phone | type | workweek | weekend....

Using a table of users and their transactions, a SQL query that shows users' first and last transaction | SQL Use Case

I took this SQL test during a job interview. The instructions are (spelling mistake is theirs): “We’d like a data model for quick lookup per user. Create a query that returns 1 row per user containing information on their first purchance and their last.” We have a table that looks like this - the table is called subscriptions which can also be considered transactions. Table "public.subscriptions" Column | Type | Collation | Nullable | Default ----------------+-----------------------------+-----------+----------+--------- transaction_id | character(36) | | not null | purchased_at | timestamp without time zone | | not null | purchase_price | double precision | | not null | user_id | character varying(255) | | not null | The way I did this was with two sub queries....

Convert seconds to HH:MM:SS PostgreSQL

Here’s how to convert a numeric integer field of seconds to HH:MM:SS. Use the INTERVAL PostgreSQL data type. The INTERVAL data type is used to store and manipulate a time period. Example SELECT 120 * interval '1 sec'; Output |120 seconds to HH:MM:SS| |-----------------------| |00:02:00| An example with a table of rows of call records that have the length of call in seconds in a column called duration. select duration , duration * interval '1 sec' seconds_to_hh_mm_ss , duration * interval '1 min' min_to_hh_mm_ss from calls; Output...