35 lines
967 B
Markdown
35 lines
967 B
Markdown
---
|
|
categories:
|
|
- Databases
|
|
- Programming Languages
|
|
tags: [SQL]
|
|
---
|
|
|
|
# SQL: Language structure
|
|
|
|
The structure or syntax of SQL is composite and mirrors that of a natural or logical language. There are overall statements (queries) which subdivide hierarchially into clauses, predicates, and expressions.
|
|
|
|
## Query
|
|
|
|
- A statement that updates or retrieves data from a table based on passed-in criteria
|
|
- The highest level in the syntax tree, equivalent to a sentence in natural language
|
|
- Examples:
|
|
- `SELECT`
|
|
- `UPDATE`
|
|
- `DELETE`
|
|
- Applied example:
|
|
- `SELECT name FROM model`
|
|
|
|
## Clause
|
|
|
|
- Typically provides parameters for a given query
|
|
- For example running a query against a specific table (`FROM`) that satisfies certain conditions (`WHERE`)
|
|
|
|
## Predicates
|
|
|
|
- A logical or numerical condition which is passed to a given clause.
|
|
- For example `WHERE` a given condition obtains
|
|
|
|
### Expression
|
|
|
|
- The lowest level of the hierarchy: field, row names etc
|