SQL CheatSheet for begineers

Data Types

Name	Parameters	Comments
`CHAR`	`(n)`	fixed length string, n being the string length, max 255
`VARCHAR`	`(n)`	variable length string, n being the max string length, if n > 255 it is converted into `TEXT` variable
`TEXT`		up to 65 535 characters
`BLOB`		up to 65 535 bytes of data
`LONGTEXT`		up to 4 294 967 295 characters
`LONGBLOB`		up to 4 294 967 295 bytes of data
`ENUM`	`(x, y, z, ...)`	list of possible values, if a value is inserted that is not in the list a blank value will be inserted, sorted in the insertion order
`SET`		similar to `ENUM` but can store more than one choice
`INT`	`(n)`	intiger, n is optional to limit a maximum size, `UNSIGNED*` for unsigned values
`BIGINT`	`(n)`	intiger, n is optional to limit a maximum size, `UNSIGNED*` for unsigned values
`FLOAT`	`(n, d)`	floating decimal, n, d are optional and limit the maximum size of the intiger and decimal part respectively
`DOUBLE`	`(n, d)`	floating decimal, n, d are optional and limit the maximum size of the intiger and decimal part respectively
`DECIMAL`	`(n, d)`	`DOUBLE` stored as a string, n, d are optional and limit the maximum size of the intiger and decimal part respectively
`DATE`	`()`	YYYY-MM-DD format
`TIME`	`()`	HH:MM:SS format
`DATETIME`	`()`	YYYY-MM-DD HH:MM:SS format
`TIMESTAMP`	`()`	number of seconds since the Unix epoch ('1970-01-01 00:00:00' UTC)
`YEAR`	`()`	can be in a 2-digit format or a 4-digit format

Condition Operators

Type	Operators	Comments
Arithmetic	`+, -, *, /`
Comparation	`=, >, <, >=, <=, <>`	`<>` operator means `!=`
Bitwise	`&, \|, ^`	AND, OR, XOR respectively
Logical	`ALL, ANY, NOT, AND, OR, BETWEEN, IN, EXISTS, LIKE, SOME`

For more details see this.

Table Creation

create table table_name
    (column_name data_type [column_restriction] [default_value])
    [, column_name data_type [column_restriction] [default_value], ...]
    table_restrictions);

Column Restrictions

Name	Parameters	Comments
`UNIQUE`		column can't have repeated values
`PRIMARY KEY`		this column is the primary key for the table
`REFERENCE`	`table [column]`	this column is a foreign key referencing said table/column
`CHECK`	`(condition ...)`	conditions can only reference self column
`NOT NULL`		this column can't contain null values

Table Restrictions

Name	Parameters	Comments
`UNIQUE`	`column ...`	this set of columns must have unique tuples
`PRIMARY KEY`	`column ...`	this set of columns are the table primary keys
`FOREIGN KEY` `REFERENCE`	`column ...` `table [column]`	this set of columns are foreign keys to the table/column referenced
`CHECK`	`(condition ...)`	conditions can only reference columns from self table

Tuple Insertion

insert into table_name [column, ...]
(values {val | NULL} [, ...] | query);

Values must be the same data types as indicated in create table and in the same order.

Tuple Deletion

delete from table_name
where condition ...;

Tuple Modification

update table_name
set column_name = {expression | NULL} [, ...]
where condition ...;

Query

Basic format

select column_name [, ...] | *
from table_name
[where condition ...];

* means select all columns from said table.

Ordered

select column_name [, ...] | *
from table_name
[where condition ...]
order by column_name [DESC | ASC] [, ...];

If not specified, it defaults to ASC.

Without repetitions

select [DISTINCT | ALL] column_name [, ...] | *
from table_name
[where condition ...];

If not specified, it defaults to ALL.

Grouping

select column_name [, ...] | *
from table_name
[where condition ...]
group by column_name [, ...]
[having condition ...];

Agregation functions

Name	Parameters	Comments
`COUNT`	`(* \| DISTINCT column_name \| column_name)`	null values are not counted
`SUM`	`expression`
`MIN`	`expression`
`MAX`	`expression`
`AVG`	`expression`

More than one table

select k.column_name [, ...] | *
from table_name k [[, | INNER JOIN | NATURAL INNER JOIN] ...]
[where condition ...]
group by k.column_name [, ...]
[having condition ...];

k is the key that indicates from which table the column is referencing to.

Query union

select k.column_name [, ...] | *
from table_name k [[, | INNER JOIN | NATURAL INNER JOIN] ...]
[where condition ...]
UNION
select k.column_name [, ...] | *
from table_name k [[, | INNER JOIN | NATURAL INNER JOIN] ...]
[where condition ...]
[order by k.column_name [DESC | ASC] [, ...]];

The two selects must be compatible, and the order by command afects both queries.

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