Basic SQL
What is SQL?
SQL stands for Structured Query Language. It is a special-purpose language used to manage data stored in relational databases. SQL allows users to:
Interact with existing databases.
Execute queries to gather insights from the data.
Define the structure of the data using schemas.
Relational Databases
Relational databases use tables of data related by common fields (relationships).
Tables: Names should be lowercase, use underscores instead of spaces, and can be collective or plural.
Fields: Columns in a table.
Names should be lowercase, without spaces, and singular.
Unique Identifier: A value that distinguishes a record from others in the same table.
Schema: A design blueprint of the database showing tables and their relationships.
Row: Represents a single entity.
Column: Represents an attribute of the entity.
MySQL data types
the most commonly used MySQL data types
INT
Integer value
123, -456
VARCHAR
Variable-length string
'hello', 'example'
TEXT
Variable-length text string
'Lorem ipsum...'
DATE
Date value
'2024-06-12'
TIMESTAMP
Date and time
'2024-06-12 10:30:45'
FLOAT
Floating-point number
3.14, -0.001
DOUBLE
Double-precision floating-point number
123.456, -987.654
BOOLEAN
Boolean value (0 for false, 1 for true)
0, 1
ENUM
Enumeration of possible values
'red', 'green'
DECIMAL
Exact numeric value with decimal precision
123.45, -9876.543
CHAR
Fixed-length character string
'abc', 'xyz'
BLOB
Binary large object, for storing binary data
Binary data
JSON
JSON data type
{"key": "value"}
TIME
Time value
'10:30:45'
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