SQL
Source of Information
Some notes here were taken while studying the first lessons of "SQL Fundamentals" from https://datacamp.com
Others were taken by demand.
SELECT with Regular Expressions
NOTE: I only tested this on MySQL.
SELECT
column_list
FROM
table_name
WHERE
string_column REGEXP pattern;
example:
SELECT
productname
FROM
products
WHERE
productname REGEXP '^(A|B|C)'
ORDER BY productname;
SELECT DISTINCT
Works like uniq in shell scripts.
SELECT COUNT()
COUNT(*)
Counts the number of rows.
COUNT(column_name)
Counts the number of no-null values in column_name.
COUNT(DISTINCT column_name)
Counts the number of distinct values in column_name.
WHERE
WHERE a BETWEEN x AND y
Checks if the value of a is between the values x and y (inclusive).
WHERE a IN (value1, value2, value3)
Checks if a is equal one of the values in the list.
SELECT a LIKE pattern / SELECT a NOT LIKE pattern
Allows using patterns for searching.
% is a wildcard fro "anything", and _ is a wildcard forr any character).