SQL
Structured Query Language
Last updated
Structured Query Language
Last updated
An entity-relationship diagram (ERD) is a common way to view how data is structured in a database.
Structured Query Language (SQL) is a language that allows us to access data stored in a database.
MySQL
Access
Oracle
Microsoft SQL Server
Postgres
SELECT: This clause specifies the columns from the data source that should be included in the query results.
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.
WHERE: This clause specifies conditions that must be met for a row to be included in the query results.
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.
HAVING: This clause is used to filter the groups in the query results, based on the values of aggregate functions applied to each group.
ORDER BY: This clause specifies the order in which the rows of the query results should be returned.
LIMIT: This clause limits the rows returned.
It is common and best practice to capitalize all SQL commands, like SELECT and FROM, and keep everything else in your query lower case.
| 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.
