SQL

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Data Description Language (DDL) Data Manipulation Language (DML) Data Control Language (DCL) Transaction Control Language (TCL)
CREATE/ALTER/DROP/TRUNCATE/RENAME SELECT/INSERT/UPDATE/DELETE GRANT/REVOKE BEGIN/COMMIT/ROLLBACK/SAVEPOINT

Query Summary

The key actions are:

SELECT [DISTINCT] ... FROM ...
UNION
[INNER|LEFT|RIGHT|OUTER] JOIN ... ON ...
WHERE ...
GROUP BY ...
HAVING ...
ORDER BY ... [ASC|DESC]
LIMIT ... OFFSET ...

INSERT INTO ... VALUES ...
UPDATE ... SET ... [WHERE ...]
DELETE ...

SELECT can be used with AS to rename a table or a column.

UNION adds the rows of different queries

HAVING allows aggregate functions. WHERE filters individual rows before the GROUP BY, while HAVING filters group rows created by the GROUP BY.

The order is in fact:

  1. FROM [UNION/JOIN]
  2. WHERE
  3. GROUP BY
  4. HAVING
  5. SELECT
  6. ORDER BY
  7. LIMIT

ORDER BY clause = e.g. ORDER BY x DESC, y NULLS FIRST

SQL:2008 LIMIT clause = OFFSET n ROWS FETCH FIRST m ROWS ONLY

Operations

We have the arithmetic operators +, -, *, /, and %.

Logical/Comparison operators include:

IS (NOT) NULL
UNIQUE?
=, <, >
<>, !=
NOT, AND, OR
BETWEEN ... AND ...
EXISTS
IN ...
LIKE ...
... ANY, ALL

BETWEEN can be numbers, texts, or dates. In the case of text it seems to use alphabetical ordering (Unicode considerations)?

EXISTS tests whether a subquery returns any values (boolean existence check).

IN can use a tuple of values ('George', 'Clooney'), or a subquery.

LIKE uses two wildcards % (0+ characters), and _ (exactly one character). For example, _r% would mean values with "r" in the 2nd position.

ANY and ALL can be used with an operator against a subquery, e.g. WHERE column = ANY (SELECT ...).

Aggregate Functions

We have aggregate functions that can act on values:

MIN
MAX
COUNT
AVG
SUM

Be aware, that the aggregate selects on the column, and will not select the entire row.

Misc.

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