More SQL notes

Databases/SQL/Create_an_SQL_table.md

@@ -9,7 +9,7 @@ tags: [SQL, relational-database]
 
 We create tables in an SQL database with the `CREATE` command.
 
-Below is an example of this in practice. Each field corresponds to a column. We specify the name of the field and its corresponding data-type. Every table must have a **primary key**. In the example, `employee_id` is the primary key.
+Below is an example of this in practice. Each field corresponds to a column. We specify the name of the field and its corresponding [data type](/Databases/SQL/Data_types_in_MySQL.md). Every table must have a **primary key**. In the example, `employee_id` is the primary key.
 
 ```sql
 CREATE TABLE employee (
@@ -26,3 +26,9 @@ CREATE TABLE employee (
     days_per_week real
     );
 ```
+
+## Check table metadata
+
+We can use `DESCRIBE [table_name]` any time we want to list out the data types and other metadata about the table.
+
+We can use `SHOW TABLE STATUS`/

Databases/SQL/Data_types_in_MySQL.md

@@ -0,0 +1,67 @@
+---
+categories:
+  - Databases
+  - Programming Languages
+tags: [SQL, relational-database]
+---
+
+# Data types in MySQL
+
+An understanding of the differences between data types is important because it obviously affects the amount of memory the database uses.
+
+## Numeric
+
+### Integer (`INT`)
+
+No fractional part, fixed number of digits
+
+### Fixed point
+
+Contains decimal point. Use when accuracy is more important that representing very large or very small values
+
+### Floating point
+
+Contains decimal point. Use when the ability to represent very large and very small values is more important than precision
+
+## String
+
+### Fixed-length character strings ()
+
+Spaces are stripped in storage but represented with a character set.
+
+An example would be `CHAR(10)` or `CHAR(3)`. Here we set the upper limit but it must be the case that no string exceeds it.
+
+### Variable-length character strings
+
+As above but allowing for variable-length strings.
+
+A common example is `VARCHAR(255)`. The 255 refers to the maximal character length, not the byte length. We must put `255` as the parameter even if our character lengths will be below this but where we don't know the minimum and maximum length.
+
+## Large object storage
+
+### Blob
+
+For storing images, audio and other binary media.
+Variants: `TINYBLOB`, `BLOB`, `MEDIUMBLOB` `LONGBLOB`
+
+### Text
+
+Like blob but has character set
+Variants: `TINYTEXT`, `TEXT`, `MEDIUMTEXT`, `LONGTEXT`
+
+## Date and time
+
+- `DATE`
+- `DATETIME`
+- `TIMESTAMP`
+
+## Speciality
+
+### Enumerations
+
+- `ENUM`: a single value from a list
+- `SET`: several values from a list
+
+## Storage limits
+
+Each row can have a maximum of 65,535 bytes.