SQL from Scratch: History, Theory, and Why It Remains the Language of Data
Few technologies have had such a long shelf life — and such a quietly pervasive influence — as SQL. While programming languages come and go with the t...
#2 SQLThe SELECT Statement: Reading Data from a Relational Database
If you ever plan to ask a question of a database, you will almost certainly begin with the word SELECT. It is the verb of SQL — the command that retri...
#3 SQLWhat Type Is That Column?
Every column in a database is, in a sense, a labelled box. The label tells the engine what may be stored inside, how much room to reserve, and how the...
#4 SQLSQL JOINs: Combining Data from Multiple Tables
Relational databases deliberately scatter information across many tables — a single customer here, their orders there, their addresses somewhere else....
#5 SQLFrom Rows to Insights: Aggregate Functions
A database that can only hand back individual rows is like a calculator that only displays the numbers you typed in. The real power of SQL appears whe...
#6 SQLQuestions Inside Questions: SQL Subqueries Explained
A subquery is a query nested inside another query — a small question whose answer feeds a larger one. Master the four places a subquery can live and y...
#7 SQLUnderstanding SQL Common Table Expressions
A Common Table Expression — or CTE — is a named temporary result set that exists only for the duration of a single query. It lets you take a complicat...
#8 SQLUnderstanding Temporary Tables
Imagine a whiteboard you wheel into a meeting. You scribble figures on it, refer back to them as the discussion unfolds, rearrange them — and when the...
#9 SQLCTE vs Temporary Table: Which One to Use and When
Two of SQL's most useful tools for handling intermediate results look deceptively similar: the Common Table Expression (CTE) and the temporary table. ...
#10 SQLWindow Functions: Compute Without Collapsing
Aggregate functions are powerful, but they come with a cost: when you ask for a summary, you lose the detail. Window functions remove that trade-off. ...
#11 SQLRanking Rows in SQL: ROW_NUMBER, RANK, DENSE_RANK, and NTILE
A window function computes a value across a set of related rows without collapsing them — each row keeps its place in the output, but gains a calculat...
#12 SQLLooking Back and Forward: LAG() and LEAD() in SQL
Most window functions look at the current row and summarise its neighbours. LAG() and LEAD() do something more direct: they reach out and grab a value...
#13 SQLWindow Frames in SQL: ROWS, RANGE, and GROUPS
Every window function operates within a window — but not every window function reads the frame. The frame is the specific subset of rows a frame-sensi...
