SQL SELECT

Internal

• SQL
• SQL WHERE

Overview

A query consists in at least one (SELECT) and at most six categories of clauses:

SELECT [one or more things] 
FROM [one or more places] 
WHERE [one or more conditions apply] 
GROUP BY [...] HAVING [...]
ORDER BY [...];

Almost every query will include at least three of these clauses (SELECT, FROM and WHERE).

Upon execution, an SQL query returns a result set.

Select all (possibly across multiple tables) then filter and discard with where.

Example

SELECT id, name FROM person WHERE id = 1;

The following query:

SELECT;

is valid, it returns one empty row.

Clauses

SELECT

SELECT [one or more things] ...

SELECT specifies which columns from the FROM sources need to be retrieved.

FROM

FROM [one or more places]

The "places" we select from can be:

• permanent
• derived
• temporary
• virtual(view)

Table alias.

Querying Multiple Tables

Querying Multiple Tables

WHERE

The WHERE Clause

GROUP BY ... HAVING

GROUP BY ... HAVING