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.
ALTER TABLE table_nameADD column_name datatype;
ALTER TABLE lets you add columns to a table in a database.
SELECT column_name(s)FROM table_nameWHERE column_1 = value_1AND column_2 = value_2;
AND is an operator that combines two conditions. Both conditions must be true for the row to be included in the result set.
SELECT column_name AS 'Alias'FROM table_name;
AS is a keyword in SQL that allows you to rename a column or table using an alias.
SELECT AVG(column_name)FROM table_name;
AVG() is an aggregate function that returns the average value for a numeric column.
SELECT column_name(s)FROM table_nameWHERE column_name BETWEEN value_1 AND value_2;
BETWEEN operator is used to filter the result set within a certain range. The values can be numbers, text or dates.
SELECT column_name,CASEWHEN condition THEN 'Result_1'WHEN condition THEN 'Result_2'ELSE 'Result_3'ENDFROM table_name;
CASE statements are used to create different outputs (usually in the
SELECT statement). It is SQL’s way of handling if-then logic.
SELECT COUNT(column_name)FROM table_name;
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
CREATE TABLE table_name (column_1 datatype,column_2 datatype,column_3 datatype);
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 FROM table_nameWHERE some_column = some_value;
DELETE statements are used to remove rows from a table.
SELECT column_name, COUNT(*)FROM table_nameGROUP BY column_name;
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.
SELECT column_name, COUNT(*)FROM table_nameGROUP BY column_nameHAVING COUNT(*) > value;
HAVING was added to SQL because the
WHERE keyword could not be used with aggregate functions.
SELECT column_name(s)FROM table_1JOIN table_2ON table_1.column_name = table_2.column_name;
An inner join will combine rows from different tables if the join condition is true.
INSERT INTO table_name (column_1, column_2, column_3)VALUES (value_1, 'value_2', value_3);
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 IS NULL;
IS NULL and
IS NOT NULL are operators used with the
WHERE clause to test for empty values.
SELECT column_name(s)FROM table_nameWHERE column_name LIKE pattern;
LIKE is a special operator used with the
WHERE clause to search for a specific pattern in a column.
SELECT column_name(s)FROM table_nameLIMIT number;
LIMIT is a clause that lets you specify the maximum number of rows the result set will have.
SELECT MAX(column_name)FROM table_name;
MAX() is a function that takes the name of a column as an argument and returns the largest value in that column.
SELECT MIN(column_name)FROM table_name;
MIN() is a function that takes the name of a column as an argument and returns the smallest value in that column.
SELECT column_nameFROM table_nameWHERE column_name = value_1OR column_name = value_2;
OR is an operator that filters the result set to only include rows where either condition is true.
SELECT column_nameFROM table_nameORDER BY column_name ASC | DESC;
ORDER BY is a clause that indicates you want to sort the result set by a particular column either alphabetically or numerically.
SELECT column_name(s)FROM table_1LEFT JOIN table_2ON table_1.column_name = table_2.column_name;
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.
SELECT ROUND(column_name, integer)FROM table_name;
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 column_nameFROM table_name;
SELECT statements are used to fetch data from a database. Every query will begin with
SELECT DISTINCT column_nameFROM table_name;
SELECT DISTINCT specifies that the statement is going to be a query that returns unique values in the specified column(s).
SELECT SUM(column_name)FROM table_name;
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 table_nameSET some_column = some_valueWHERE some_column = some_value;
UPDATE statements allow you to edit rows in a table.
SELECT column_name(s)FROM table_nameWHERE column_name operator value;
WHERE is a clause that indicates you want to filter the result set to include only rows where the following condition is true.
WITH temporary_name AS (SELECT *FROM table_name)SELECT *FROM temporary_nameWHERE column_name operator value;
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 clause is also known as common table expression (CTE) and subquery factoring.