Reference · 19 terms
Glossary
Every short form used across the series. Inside a lesson, hover or tap any dotted term to see the same entry in place.
SQL
- B-treeB-tree index
- The default index type. It keeps keys sorted so lookups, ranges and sorting are fast.Lesson 5 →
- constraintConstraint
- A rule the database enforces, such as NOT NULL, UNIQUE, CHECK or a foreign key.Lesson 4 →
- covering indexCovering index
- An index that holds every column a query needs, so the table itself is not read.Lesson 5 →
- CTECTE (common table expression)
- A named temporary result defined with WITH, used to make a big query readable.Lesson 3 →
- deadlockDeadlock
- Two transactions each wait for a lock the other holds. PostgreSQL stops one with an error.Lesson 6 →
- expand and contractExpand and contract
- A safe migration style: add the new thing, move readers and writers, then remove the old thing.Lesson 7 →
- EXPLAINEXPLAIN
- Shows the plan PostgreSQL chose for a query. With ANALYZE it also runs the query and shows real times.Lesson 5 →
- foreign keyForeign key
- A column that points to the primary key of another table and keeps the link valid.Lesson 1 →
- GROUP BYGROUP BY
- Collapses rows into groups so aggregate functions can run on each group.Lesson 2 →
- HAVINGHAVING
- Filters groups after aggregation, while WHERE filters rows before it.Lesson 2 →
- inner joinInner join
- Keeps only the rows that have a match in both tables.Lesson 1 →
- isolation levelIsolation level
- How much one transaction can see of another's work: read committed, repeatable read or serializable.Lesson 6 →
- JSONBJSONB
- A binary JSON column type that can be indexed and queried.Lesson 7 →
- left joinLeft join
- Keeps every row of the left table, with NULLs where the right table has no match.Lesson 1 →
- normalisationNormalisation
- Organising tables so each fact is stored once, which avoids update mistakes.Lesson 4 →
- NULLNULL
- A marker for 'unknown or missing'. Comparisons with NULL are neither true nor false, so use IS NULL.Lesson 0 →
- primary keyPrimary key
- A column (or columns) that uniquely identifies each row in a table.Lesson 1 →
- transactionTransaction
- A group of statements that succeed or fail together.Lesson 6 →
- window functionWindow function
- A function that computes over a set of related rows without collapsing them, such as ROW_NUMBER or LAG.Lesson 3 →