SQL

Structured Query Language

An entity-relationship diagram (ERD) is a common way to view how data is structured in a database.

Parch & Posey Database ERD

Structured Query Language (SQL) is a language that allows us to access data stored in a database.

Types of SQL Databases

1. MySQL

2. Access

3. Oracle

4. Microsoft SQL Server

5. Postgres

SQLite vs MySQL vs PostgreSQL: A Comparison Of Relational Database Management Systems | DigitalOceanDigitalOcean

Clauses

1. SELECT: This clause specifies the columns from the data source that should be included in the query results.

2. FROM: This clause specifies the data source(s) that should be queried. This can be a table, a view, or the results of another query.

3. WHERE: This clause specifies conditions that must be met for a row to be included in the query results.

4. GROUP BY: This clause groups the rows of the query results by the values in one or more columns, allowing aggregate functions to be applied to each group.

5. HAVING: This clause is used to filter the groups in the query results, based on the values of aggregate functions applied to each group.

6. ORDER BY: This clause specifies the order in which the rows of the query results should be returned.

7. LIMIT: This clause limits the rows returned.

Query Execution Order

Order	Clause	Function
1	FROM	Tables are joined to get the base data.
2	WHERE	The base data is filtered.
3	GROUP BY	The filtered base data is grouped.
4	HAVING	The grouped base data is filtered.
5	SELECT	The final data is returned.
6	ORDER BY	The final data is sorted.
7	LIMIT	The returned data is limited to row count.

Query Plans in SQL Server - Essential SQLEssential SQL

It is common and best practice to capitalize all SQL commands, like SELECT and FROM, and keep everything else in your query lower case.

Resources

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