update sql

cspell_dict_bash.txt

@@ -502,4 +502,7 @@ Goroutines
 mysqladmin
 devel
 mariadb
-SAVEPOINT
+SAVEPOINT
+smallint
+tinyint
+varchar

docs/source/reference/database/sql.md

@@ -6,6 +6,8 @@ A standard of ANSI.
 
 Almost all relational database management systems use SQL.
 
+This reference focuses on MySQL.
+
 ## What Can SQL Do
 
 * Query database
@@ -82,4 +84,94 @@ ROLLBACK
 
 ## Relational
 
-Data are stored using tables (row and column) with specified relationships between them.
+Data are stored using tables (row and column) with specified relationships between them.
+
+## Database Management
+
+Create
+
+```sql
+CREATE DATABASE aaa;
+```
+
+Delete
+
+```sql
+DROP DATABASE aaa;
+```
+
+## Table
+
+Each column is an attribute
+
+Each row is a record
+
+Common Data Types
+
+| Data Type                                                 | Usage                              |
+| --------------------------------------------------------- | ---------------------------------- |
+| integer(size) or int(size), smallint(size), tinyint(size) | store integers (exact value)       |
+| decimal(size,d), numeric(size,d)                          | fixed-point (exact value)          |
+| float, double                                             | floating-point (approximate value) |
+| char(size)                                                | fixed-length                       |
+| varchar(size)                                             | variable-length                    |
+| date                                                      | date                               |
+
+[MySQL Data Types](https://dev.mysql.com/doc/refman/8.0/en/data-types.html)
+
+`char(10)` means a string with length 10.
+
+`varchar(10)` where 10 is the max length. Usually 100 or 255.
+
+Must provide data type when creating the tables.
+
+Create a table
+
+* Usually there is a "ID" column.
+* the last column does not need a comma
+* [MySQL :: MySQL 8.0 Reference Manual :: 13.1.20 CREATE TABLE Syntax](https://dev.mysql.com/doc/refman/8.0/en/create-table.html)
+
+```sql
+CREATE TABLE some_table_name
+(
+some_col_name some_data_type,
+some_col_name some_data_type,
+some_col_name some_data_type,
+...
+);
+```
+
+Check table
+
+```sql
+DESCRIBE aaa;
+DESC aaa;
+```
+
+In the output of `DESC`,
+
+* Field means the column names, i.e. the attributes
+* Type is type
+* Null is if the cells in this column can be Null
+* Key is whether this column will be used as a key column
+* Default is the default value
+
+Delete table
+
+```sql
+DROP aaa;
+```
+
+Modify table
+
+```sql
+ALTER TABLE aaa RENAME bbb;
+
+ALTER TABLE aaa ADD ccc some_type;
+
+ALTER TABLE aaa DROP COLUMN ccc;
+
+ALTER TABLE aaa MODIFY ccc some_new_type;
+
+ALTER TABLE aaa CHANGE COLUMN ccc some_new_name some_new_type;
+```