SQL basics.

What SQL does

  • Insert/Delete/Update/Select
  • Create DB/Table/View
  • Create Stored Procedures
  • Set Permissions

SQL knowledge

  • Case insensitive
  • Semicolon after statement (some optional)

Most common statements

  • SELECT
  • UPDATE
  • DELETE
  • INSERT INTO
  • CREATE DATABASE
  • ALTER DATABASE
  • CREATE TABLE
  • ALTER TABLE
  • DROP TABLE
  • CREATE INDEX
  • DROP INDEX

SELECT statement

SELECT * FROM table_name;

SELECT column_name,column_name
FROM table_name;

SELECT DISTINCT column_name,column_name
FROM table_name;

WHERE clause

SELECT column_name,column_name
FROM table_name
WHERE column_name operator value;

operators:
=           => equal
<>          => not equal (!=)
>           => greater than
<           => less than
>=          => greater than or equal
<=          => less than or equal
BETWEEN     => between an inclusive range
LIKE        => search for a pattern
IN          => specify multiple possible values for a column

AND         => both condition true
OR          => either condition true

ORDER BY keyword

SELECT column_name,column_name
FROM table_name
ORDER BY column_name ASC|DESC, column_name ASC|DESC;

INSERT INTO statement

INSERT INTO table_name
VALUES (value1,value2,value3,...);

INSERT INTO table_name (column1,column2,column3,...)
VALUES (value1,value2,value3,...);

UPDATE statement

UPDATE table_name
SET column1=value1,column2=value2,...
WHERE some_column=some_value;

DELETE statement

DELETE FROM table_name
WHERE some_column=some_value;

=> delete all:
DELETE FROM table_name;
or
DELETE * FROM table_name;

SELECT TOP clause

=> ms sqlserver/access style:
SELECT TOP number/percent column_name(s)
FROM table_name

=> mysql style:
SELECT column_name(s)
FROM table_name
LIMIT number;

=> oracle style:
SELECT column_name(s)
FROM table_name
WHERE ROWNUM <= number;

Common operators

=> LIKE operator
SELECT column_name(s)
FROM table_name
WHERE column_name LIKE pattern;

=> NOT LIKE operator
SELECT column_name(s)
FROM table_name
WHERE column_name NOT LIKE pattern;

=> WILDCARDS chars:
%            => zero or more chars
_            => single char
[charlist]   => sets and ranges of chars
[^charlist]  => not within sets or ranges of chars
[!charlist]  => same as [^charlist]

=> IN operator
SELECT column_name(s)
FROM table_name
WHERE column_name IN (value1,value2,...);

=> BETWEEN operator
SELECT column_name(s)
FROM table_name
WHERE column_name BETWEEN value1 AND value2;

=> NOT BETWEEN operator
SELECT column_name(s)
FROM table_name
WHERE column_name NOT BETWEEN value1 AND value2;

Aliases

SELECT column_name AS alias_name
FROM table_name;

SELECT column_name(s)
FROM table_name AS alias_name;

JOINS

=> INNER JOIN
SELECT column_name(s)
FROM table1
INNER JOIN table2
ON table1.column_name=table2.column_name;

SELECT column_name(s)
FROM table1
JOIN table2
ON table1.column_name=table2.column_name;

=> LEFT JOIN
SELECT column_name(s)
FROM table1
LEFT JOIN table2
ON table1.column_name=table2.column_name;

SELECT column_name(s)
FROM table1
LEFT OUTER JOIN table2
ON table1.column_name=table2.column_name;

=> RIGHT JOIN
SELECT column_name(s)
FROM table1
RIGHT JOIN table2
ON table1.column_name=table2.column_name;

SELECT column_name(s)
FROM table1
RIGHT OUTER JOIN table2
ON table1.column_name=table2.column_name;

=> FULL OUTER JOIN
SELECT column_name(s)
FROM table1
FULL OUTER JOIN table2
ON table1.column_name=table2.column_name;

UNION operator

=> only distinct results
SELECT column_name(s) FROM table1
UNION
SELECT column_name(s) FROM table2

=> with duplicate results
SELECT column_name(s) FROM table1
UNION ALL
SELECT column_name(s) FROM table2

SELECT INTO statement

SELECT *
INTO newtable [IN externaldb]
FROM table1;

SELECT column_name(s)
INTO newtable [IN externaldb]
FROM table1;

INSERT INTO SELECT statement

INSERT INTO table2
SELECT * FROM table1;

INSERT INTO table2
(column_name(s))
SELECT column_name(s)
FROM table1;

CREATE statement

=> create db:
CREATE DATABASE dbname;

=> create table:
CREATE TABLE table_name
(
column_name1 data_type(size) constraint_name,
column_name2 data_type(size) constraint_name,
column_name3 data_type(size) constraint_name,
...
);

constraints can be:
- NOT NULL
- UNIQUE
- PRIMARY KEY (AUTO_INCREMENT)
- FOREIGN KEY (REFERENCES)
- CHECK
- DEFAULT

CREATE INDEX statement

CREATE INDEX index_name
ON table_name (column_name)

CREATE UNIQUE INDEX index_name
ON table_name (column_name)

DROP statement

=> drop index
DROP INDEX index_name ON table_name (access)
DROP INDEX table_name.index_name (sqlserver)
DROP INDEX index_name (db2/oracle)
ALTER TABLE table_name DROP INDEX index_name (mysql)

=> drop table
DROP TABLE table_name

=> drop db
DROP DATABASE db_name

=> delete table data only
TRUNCATE TABLE table_name

CREATE VIEW statement

CREATE VIEW view_name AS
SELECT column_name(s)
FROM table_name
WHERE condition

CREATE OR REPLACE VIEW view_name AS
SELECT column_name(s)
FROM table_name
WHERE condition

DROP VIEW view_name

Data types

=> null type:
IS NULL     => test if column is null
IS NOT NULL => test if column is not null
=> general types:
- CHARACTER
- VARCHAR
- BINARY
- BOOLEAN
- INTEGER
- BIGINT
- NUMERIC
- FLOAT
- DATE
- TIME
- TIMESTAMP
- etc.

References

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