SQL Commands - Codecademy

Background

SQL, Structured Query Language, is a programming language designed to manage data stored in relational databases. SQL operates through simple, declarative statements. This keeps data accurate and secure, and it helps maintain the integrity of databases, regardless of size.

Here’s an appendix of commonly used commands.

Commands

ALTER TABLE

ALTERTABLE table_name ADD column_name datatype;Copy to clipboardCopy to clipboard

ALTER TABLE lets you add columns to a table in a database.

AND

SELECT column_name(s)FROM table_nameWHERE column_1 = value_1AND column_2 = value_2;Copy to clipboardCopy to clipboard

AND is an operator that combines two conditions. Both conditions must be true for the row to be included in the result set.

AS

SELECT column_name AS'Alias'FROM table_name;Copy to clipboardCopy to clipboard

AS is a keyword in SQL that allows you to rename a column or table using an alias.

AVG()

SELECTAVG(column_name)FROM table_name;Copy to clipboardCopy to clipboard

AVG() is an aggregate function that returns the average value for a numeric column.

BETWEEN

SELECT column_name(s)FROM table_nameWHERE column_name BETWEEN value_1 AND value_2;Copy to clipboardCopy to clipboard

The BETWEEN operator is used to filter the result set within a certain range. The values can be numbers, text or dates.

CASE

SELECT column_name,CASEWHEN condition THEN'Result_1'WHEN condition THEN'Result_2'ELSE'Result_3'ENDFROM table_name;Copy to clipboardCopy to clipboard

CASE statements are used to create different outputs (usually in the SELECT statement). It is SQL’s way of handling if-then logic.

COUNT()

SELECTCOUNT(column_name)FROM table_name;Copy to clipboardCopy to clipboard

COUNT() is a function that takes the name of a column as an argument and counts the number of rows where the column is not NULL.

CREATE TABLE

CREATETABLE table_name ( column_1 datatype, column_2 datatype, column_3 datatype);Copy to clipboardCopy to clipboard

CREATE TABLE creates a new table in the database. It allows you to specify the name of the table and the name of each column in the table.

DELETE

DELETEFROM table_nameWHERE some_column = some_value;Copy to clipboardCopy to clipboard

DELETE statements are used to remove rows from a table.

GROUP BY

SELECT column_name,COUNT(*)FROM table_nameGROUPBY column_name;Copy to clipboardCopy to clipboard

GROUP BY is a clause in SQL that is only used with aggregate functions. It is used in collaboration with the SELECT statement to arrange identical data into groups.

HAVING

SELECT column_name,COUNT(*)FROM table_nameGROUPBY column_nameHAVINGCOUNT(*)>value;Copy to clipboardCopy to clipboard

HAVING was added to SQL because the WHERE keyword could not be used with aggregate functions.

INNER JOIN

SELECT column_name(s)FROM table_1JOIN table_2ON table_1.column_name = table_2.column_name;Copy to clipboardCopy to clipboard

An inner join will combine rows from different tables if the join condition is true.

INSERT

INSERTINTO table_name (column_1, column_2, column_3)VALUES(value_1,'value_2', value_3);Copy to clipboardCopy to clipboard

INSERT statements are used to add a new row to a table.

IS NULL / IS NOT NULL

SELECT column_name(s)FROM table_nameWHERE column_name ISNULL;Copy to clipboardCopy to clipboard

IS NULL and IS NOT NULL are operators used with the WHERE clause to test for empty values.

LIKE

SELECT column_name(s)FROM table_nameWHERE column_name LIKE pattern;Copy to clipboardCopy to clipboard

LIKE is a special operator used with the WHERE clause to search for a specific pattern in a column.

LIMIT

SELECT column_name(s)FROM table_nameLIMIT number;Copy to clipboardCopy to clipboard

LIMIT is a clause that lets you specify the maximum number of rows the result set will have.

MAX()

SELECTMAX(column_name)FROM table_name;Copy to clipboardCopy to clipboard

MAX() is a function that takes the name of a column as an argument and returns the largest value in that column.

MIN()

SELECTMIN(column_name)FROM table_name;Copy to clipboardCopy to clipboard

MIN() is a function that takes the name of a column as an argument and returns the smallest value in that column.

OR

SELECT column_nameFROM table_nameWHERE column_name = value_1OR column_name = value_2;Copy to clipboardCopy to clipboard

OR is an operator that filters the result set to only include rows where either condition is true.

ORDER BY

SELECT column_nameFROM table_nameORDERBY column_name ASC|DESC;Copy to clipboardCopy to clipboard

ORDER BY is a clause that indicates you want to sort the result set by a particular column either alphabetically or numerically.

OUTER JOIN

SELECT column_name(s)FROM table_1LEFTJOIN table_2ON table_1.column_name = table_2.column_name;Copy to clipboardCopy to clipboard

An outer join will combine rows from different tables even if the join condition is not met. Every row in the left table is returned in the result set, and if the join condition is not met, then NULL values are used to fill in the columns from the right table.

ROUND()

SELECTROUND(column_name,integer)FROM table_name;Copy to clipboardCopy to clipboard

ROUND() is a function that takes a column name and an integer as arguments. It rounds the values in the column to the number of decimal places specified by the integer.

SELECT

SELECT column_name FROM table_name;Copy to clipboardCopy to clipboard

SELECT statements are used to fetch data from a database. Every query will begin with SELECT.

SELECT DISTINCT

SELECTDISTINCT column_nameFROM table_name;Copy to clipboardCopy to clipboard

SELECT DISTINCT specifies that the statement is going to be a query that returns unique values in the specified column(s).

SUM

SELECTSUM(column_name)FROM table_name;Copy to clipboardCopy to clipboard

SUM() is a function that takes the name of a column as an argument and returns the sum of all the values in that column.

UPDATE

UPDATE table_nameSET some_column = some_valueWHERE some_column = some_value;Copy to clipboardCopy to clipboard

UPDATE statements allow you to edit rows in a table.

WHERE

SELECT column_name(s)FROM table_nameWHERE column_name operator value;Copy to clipboardCopy to clipboard

WHERE is a clause that indicates you want to filter the result set to include only rows where the following condition is true.

WITH

WITH temporary_name AS(SELECT*FROM table_name)SELECT*FROM temporary_nameWHERE column_name operator value;Copy to clipboardCopy to clipboard

WITH clause lets you store the result of a query in a temporary table using an alias. You can also define multiple temporary tables using a comma and with one instance of the WITH keyword.

The WITH clause is also known as common table expression (CTE) and subquery factoring.