sql.md

Using String as Primary Key

reference: https://stackoverflow.com/questions/3455297/mysql-using-string-as-primary-key

There's nothing wrong with using a CHAR or VARCHAR as a primary key.

Sure it'll take up a little more space than an INT in many cases, but there are many cases where it is the most logical choice and may even reduce the number of columns you need, improving efficiency, by avoiding the need to have a separate ID field.

What is the difference between a primary key and a index key

reference: https://stackoverflow.com/questions/5374908/what-is-the-difference-between-a-primary-key-and-a-index-key

A primary key is a special kind of index in that:

• there can be only one;
• it cannot be nullable; and
• it must be unique.

MySQL string sorting

reference: https://stackoverflow.com/a/8557307

Alpha Numeric Sorting in MySQL

Given input

1A 1a 10A 9B 21C 1C 1D

Expected output

1A 1C 1D 1a 9B 10A 21C

Query

-- Bin Way
-- ===================================
SELECT 
tbl_column, 
BIN(tbl_column) AS binray_not_needed_column
FROM db_table
ORDER BY binray_not_needed_column ASC , tbl_column ASC

-----------------------

-- Cast Way
-- ===================================
SELECT 
tbl_column, 
CAST(tbl_column as SIGNED) AS casted_column
FROM db_table
ORDER BY casted_column ASC , tbl_column ASC

Natural Sorting in MySQL

Given input

Table: sorting_test
 -------------------------- -------------
| alphanumeric VARCHAR(75) | integer INT |
 -------------------------- -------------
| test1                    | 1           |
| test12                   | 2           |
| test13                   | 3           |
| test2                    | 4           |
| test3                    | 5           |
 -------------------------- -------------

Expected Output

 -------------------------- -------------
| alphanumeric VARCHAR(75) | integer INT |
 -------------------------- -------------
| test1                    | 1           |
| test2                    | 4           |
| test3                    | 5           |
| test12                   | 2           |
| test13                   | 3           |
 -------------------------- -------------

Query

SELECT alphanumeric, integer
       FROM sorting_test
       ORDER BY LENGTH(alphanumeric), alphanumeric  

Sorting of numeric values mixed with alphanumeric values

Given input

2a, 12, 5b, 5a, 10, 11, 1, 4b

Expected Output

1, 2a, 4b, 5a, 5b, 10, 11, 12

Query

SELECT version
FROM version_sorting
ORDER BY CAST(version AS UNSIGNED), version;