Unique Identifier in a Database
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A value that uniquely identifies a record in a database table.
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Relationships in Databases
Connections between tables in a database, typically defined by keys.
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A One-to-many (Many-to-one) Relationship
A type of relationship in a database where a record in one table can be associated with one or more records in another table.
Many-to-one is the reverse of one-to-many.
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A One-to-one Relationship
A type of relationship in a database where one record in a table is associated with one and only one record in another table.
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A Many-to-many Relationship
A type of relationship in a database where multiple records in one table can be associated with multiple records in another table and vice versa.
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Cardinality Constraints
Restrictions that define the number of instances that one entity can be associated with another entity in a relationship.
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Primary Key
A column (or set of columns) in a table that uniquely identifies each row.
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Foreign Key
A column (or set of columns) in a table whose values match the values of a column (or a set of columns) in another table from the database.
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Unique Key
A field attribute ensuring no duplicate values within a column. Different from the primary key, a unique key can store a null value, but only one. A table can have multiple unique keys while it can have only one primary key. Unique keys allow modification and deletion of data, unlike primary keys.
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Composite Key
A key that consists of two or more fields that are used together to uniquely identify a record in a table.
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Null Value in Primary Key
A state that is not allowed in a primary key column, as primary keys must have a unique and non-null value for each row.
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Base Tables
Tables in a database that physically store data, as opposed to views or derived tables which only refer to data physically stored in the base tables.
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Child Table
A table in a database that has a foreign key referencing the primary key of another table.
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Parent Table
A table in a database referenced by the foreign key in another table.
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Referencing Table
A table in a database that includes a foreign key pointing to uniquely identified rows in another table.
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Referenced Table
A table in a database containing uniquely identified rows to which another table's foreign key points.
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Storage
The physical or virtual space used by a database to save data, with various mechanisms
in place to optimize performance and ensure data integrity.
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Storage Size
The amount of disk space that a database object or an entire database occupies in SQL.
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Precision
The number of digits in a number.
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Scale
The number of digits to the right of the decimal point in a number.
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Triggers
Database objects that automatically execute a predefined action when а certain data modification operation occurs.
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BEFORE Trigger
A database trigger that executes before one or more specified data modification operations occur.
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AFTER Trigger
A database trigger that executes after a specified data modification operation.
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Query
A request for data from a database table or combination of tables. Information from the database can be retrieved and sorted in a variety of ways by writing the relevant queries.
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Subquery (or nested query)
A query nested within another SQL query.
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Query Optimization
The process of modifying a query to improve its efficiency and performance expressed in terms
of augmented speed of data retrieval and reduced resource consumption.
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Query efficiency
A performance measure of a SQL query regarding speed and resource utilization.
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Partitioning
Database partitioning (or data partitioning) is a database technique to divide a subset of the database data into separate chunks (or namely - partitions), that are yet being treated as a single data table. The idea behind using data partitions is that they can be stored, accessed, or managed one by one.
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Variable
A placeholder used in programming and databases to store a value that can change
during the execution of a program or query.
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Local Variables
Variables declared within a stored routine in SQL, accessible only within that routine.
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Session Variables
Variables that are defined by the user and that can be accessed during a single session in a database.
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Global Variables
Variables in a database that are accessible throughout the entirety of the server (i.e. that are available and maintained across different sessions).
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DECLARE
Keyword used for creating local variables in MySQL.
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SET Statement
A statement used for creating Session Variables in MySQL
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Statement Terminator (in SQL)
A character or sequence of characters that indicate the end of an SQL statement.
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Alphanumeric Data Types
Data types in SQL that can store both letters (alphabets) and numbers, but no other characters (such as punctuation marks or other symbols, for instance).
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String
A sequence of characters used in programming and databases to represent text rather than numbers.
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Length
In databases, "length" refers to the number of characters contained in a string.
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Bytes
A unit of digital information in computing and telecommunications.
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CHAR
A fixed-length character data type in SQL.
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VARCHAR
A variable-length character data type in SQL.
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ENUM
An SQL data type consisting of a set of named VALUES (NULL,ref. "enumeration").
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Fixed-Storage Data Type
A data type in SQL having a fixed-space allocation.
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Numeric Data Types
SQL data types representing numeric values.
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Integer (INT)
An SQL data type for storing whole numbers.
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TINYINT
An SQL data type for integers ranging from -128 to 127 inclusive.
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SMALLINT
An SQL data type for small-range integers (i.e. integers ranging from -32,767 to 32,767 inclusive).
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MEDIUMINT
An SQL data type for medium-range integers (i.e. integers ranging from -8388608 to 8388607 inclusive).
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BIGINT
An SQL data type for large-range integers (i.e. integers ranging from approx. -9 to 9 quintillion).
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Fixed-point Data Types
A numeric SQL data type with fixed decimal points.
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DOUBLE
An SQL data type used for storing precise numeric values with floating point precision.
It can hold both very large and very small values.
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DECIMAL
An SQL data type for fixed-point numbers.
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DATE
An SQL data type for storing date and time as a number.
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DATETIME
An SQL data type for storing dates only.
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UNIX_TIMESTAMP()
An SQL data type for storing both dates and time.
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BLOB (Binary Large Object)
An SQL data type for storing both date and time.
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Boolean Value
A value for storing date and time as a number.
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Constraints
A value that is either TRUE, FALSE, or NULL.
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NOT NULL
A constraint ensuring that a column cannot have a NULL value.
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Unique Constraint
A constraint ensuring that all values in a column are the same.
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DEFAULT Constraint
Sets a default value for a row even when a value is specified.
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Auto-increment
A property used in SQL to automatically generate a unique value for a column,
typically a primary key, with each new record insertion.
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Keywords in SQL
Reserved words in SQL used to perform operations and define the structure of SQL commands.
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Reserved Words
Words in SQL that don’t have a specific meaning and function, and can be used as identifiers like table or column names.
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Reserved Words
Words in SQL that don’t have a specific meaning and function, and can be used as identifiers like table or column names.
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Reserved Words
Words in SQL that have a specific meaning and function, and cannot be used as identifiers like table or column names.
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Primary Key vs. Unique Key
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SQL Data Types
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Signed vs. Unsigned Values
In SQL, signed values can be positive or negative, whereas unsigned values can only be positive.
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Keys vs. Constraint (SQL)
In the context of SQL, "keys" refer to creating relationships between separate tables or views within a database. "Constraints" refer to specifying the rules for the data in a given table.
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Foreign Key Constraint