Data & Storage/Data & services

SQL

9 micro-topics in Data & Storage, each with the evidence that proves you have it and the written reason behind every link. Nothing outside this domain sits under it — you can start here. Downstream, it holds up 3 domains.

9 topics · depth 0–4 of 16 · 8 internal links · 0 in · 5 out

Prerequisites · 0 links in

Before you start

Load-bearing links first. Each one says what in this domain rests on what outside it, and why.

Nothing outside this domain sits under it. It is an entry point — you can start here.

9 topics · depth 0–4

What you will be able to do

In prerequisite order. Each idea names the artifact that closes it, the market demand that put it on the map, and what it stands on.

Depth 0 · procedural · unassisted · M07 §7.2

Query rows with SELECT

Projects, filters and orders result sets

Evidence: Answers a question from one table without help
Market anchor: SQL
Rests on: Nothing sits under this one — it is an entry point.

Depth 1 · conceptual · unassisted · M07 §7.2

Join across tables

Chooses inner, left and the join key

Evidence: Answers a business question spanning three tables
Market anchor: SQL
Rests on: load-bearing
Query rows with SELECT
A join extends a select across tables.

Depth 1 · procedural · unassisted · M07 §7.2

Insert, update and delete safely

Writes mutations with a WHERE that is verified first

Evidence: Runs a mutation in a transaction after checking the row count
Market anchor: SQL
Rests on: load-bearing
Query rows with SELECT
A safe mutation starts as a verified select.

Depth 2 · procedural · unassisted · M07 §7.2

Aggregate and group

Applies GROUP BY, HAVING and aggregate functions

Evidence: Produces a correct grouped report
Market anchor: SQL · analytics
Rests on: load-bearing
Join across tables
Grouping usually operates on joined results.

Depth 2 · conceptual · scaffolded · M07 §7.2

Use transactions

Groups statements into an atomic unit

Evidence: Rolls back a partial failure cleanly
Market anchor: SQL · databases
Rests on: load-bearing
Insert, update and delete safely
Transactions group mutations.

Depth 2 · conceptual · scaffolded · M07 §7.2

Reason about indexes

Knows what an index costs and what it buys

Evidence: Explains a slow query from its plan
Market anchor: Databases · performance
Rests on: load-bearing
Join across tables
Index cost is felt on joins and filters.

Depth 3 · conceptual · scaffolded · M07 §7.2

Compose subqueries and CTEs

Builds readable multi-step queries

Evidence: Rewrites a nested query as a readable CTE chain
Market anchor: SQL
Rests on: load-bearing
Aggregate and group
CTEs organize multi-step aggregation.

Depth 3 · meta · guided · M07 §7.2

Read a query plan

Interprets what the database will actually do

Evidence: Identifies a sequential scan and fixes it
Market anchor: Databases · performance
Rests on: load-bearing
Reason about indexes
A plan is read in terms of index use.

Depth 4 · conceptual · guided · M07 §7.2

Apply window functions

Ranks and aggregates over partitions

Evidence: Produces a running total or per-group rank
Market anchor: SQL · analytics
Rests on: load-bearing
Compose subqueries and CTEs
Window functions extend grouped computation.

Unlocks · 5 links out