What’s on the SQL Aggregates poster
A 6-row table: Function · Ignores NULL? · Note.
Every non-aggregated column in SELECT must also appear in GROUP BY.
- COUNT(*) — no — Counts rows
- COUNT(col) — yes — Counts non-null values
- SUM(col) — yes — NULL if no rows
- AVG(col) — yes — Excludes nulls from the divisor
- MIN / MAX — yes — Works on text and dates too
- STRING_AGG — yes — Joins values into one string
COUNT(*) and COUNT(column) differ whenever the column is nullable, and that difference is often the bug.
Questions about the SQL Aggregates poster
- What’s on the SQL Aggregates poster?
- A 6-row table: Function · Ignores NULL? · Note. Every non-aggregated column in SELECT must also appear in GROUP BY. COUNT(*) — no — Counts rows; COUNT(col) — yes — Counts non-null values; SUM(col) — yes — NULL if no rows; AVG(col) — yes — Excludes nulls from the divisor; MIN / MAX — yes — Works on text and dates too; STRING_AGG — yes — Joins values into one string. COUNT(*) and COUNT(column) differ whenever the column is nullable, and that difference is often the bug.
- Who is the SQL Aggregates poster for?
- SQL Aggregates belongs to the Computing section rather than to a school year, because computing is not something one grade owns. Anyone learning languages can pin it up — a beginner, a student mid-course, or someone revising years later.
- When should you use the SQL Aggregates poster?
- WHERE filters rows before grouping; HAVING filters groups after. Putting one in the other's place is the classic error. A wall chart earns its place by being glanceable from where the work is happening, so SQL Aggregates belongs on the wall where that computing work actually happens, within glancing distance, rather than filed away.
- What other posters go with SQL Aggregates?
- REST API Design, Bash Scripting and Error Handling sit alongside SQL Aggregates in the Computing section. Printed together they make a wall rather than a single sheet, which is how a reference set actually gets used.REST API DesignBash ScriptingError Handling
- Is the SQL Aggregates poster free to download and print?
- Yes. SQL Aggregates downloads as a free PDF with no account, no email and no watermark, like everything else in the Computing section. Print as many copies as you like for a home, a classroom, a library or a tutoring group; reselling the file is the only thing the licence rules out.Read the licence
- What size does the SQL Aggregates poster print at?
- SQL Aggregates is a vector PDF laid out for US Letter, and prints on A4 with Fit to page — the same file, no separate download. Because every mark on it is drawn rather than photographed, it stays sharp enlarged to A3, A2 or A1 at a copy shop. Colour carries emphasis only, so a greyscale print of SQL Aggregates loses nothing.Printing guide
Related posters
Charts that sit alongside SQL Aggregates on the same wall.
Browse every Computing poster, or start from the full catalogue.