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What is a surrogate key?
A surrogate key is a field in a table that has been created solely for the purpose of being the primary key. It has no other purpose than internal storage and reference number. For example, a customer may have an account number that is unique to them, but a customer_id field might be created on theRead more
A surrogate key is a field in a table that has been created solely for the purpose of being the primary key. It has no other purpose than internal storage and reference number.
For example, a customer may have an account number that is unique to them, but a customer_id field might be created on the table and used as the primary key, in case business rules change and mean that the account number is no longer unique.
See lessWhat is a composite key?
A composite key is a primary key that is made up of two or more fields. Often, primary keys are single fields, but in some cases, a row is identified by multiple fields. This is what a composite key is.
A composite key is a primary key that is made up of two or more fields. Often, primary keys are single fields, but in some cases, a row is identified by multiple fields. This is what a composite key is.
See lessWhat is a foreign key?
A foreign key is a field in a table that refers to a primary key in another table. It is used to link the record in the first table to the record in the second table.
A foreign key is a field in a table that refers to a primary key in another table. It is used to link the record in the first table to the record in the second table.
See lessWhat is a primary key?
A primary key is a column or set of columns that uniquely identifies a row in a table. It’s created on a table and ensures that the values in that column or columns must be unique and not NULL. This is often done using some kind of numeric ID field but doesn’t have to be.
A primary key is a column or set of columns that uniquely identifies a row in a table. It’s created on a table and ensures that the values in that column or columns must be unique and not NULL.
This is often done using some kind of numeric ID field but doesn’t have to be.
See lessWhat’s the difference between a view and a materialized view?
A view is simply an SQL query that is stored on the database, without the results. Every time a view is queried, this definition of the view’s query is run. If the underlying tables have been updated, the view will load these results. A materialized view is a query where the results have been storedRead more
A view is simply an SQL query that is stored on the database, without the results. Every time a view is queried, this definition of the view’s query is run. If the underlying tables have been updated, the view will load these results.
A materialized view is a query where the results have been stored in a permanent state, like a table. If the underlying tables are updated, then by default, the materialized views are not updated.
See lessWhat is a view? When would you use one?
A view is a database object that allows you to run a saved query to view a set of data. You create a view by specifying a SELECT query to be used as the view, and then the view can be queried just like a table. There are several reasons to use a view, such as to improve to security, create a layer oRead more
A view is a database object that allows you to run a saved query to view a set of data. You create a view by specifying a SELECT query to be used as the view, and then the view can be queried just like a table.
There are several reasons to use a view, such as to improve to security, create a layer of abstraction between the underlying tables and applications, and to simplify queries.
See lessWhat is the purpose of the IN keyword?
The IN keyword allows you to check if a value matches one of a range of values. It’s often used with subqueries that return more than one row.
The IN keyword allows you to check if a value matches one of a range of values. It’s often used with subqueries that return more than one row.
See lessWhat is the purpose of the BETWEEN keyword?
The BETWEEN keyword allows you to check that a value falls in between two other values in the WHERE clause. It’s the same as checking if a value is greater than or equal to one value, and less than or equal to another value.
The BETWEEN keyword allows you to check that a value falls in between two other values in the WHERE clause.
It’s the same as checking if a value is greater than or equal to one value, and less than or equal to another value.
See lessWhat are the different DML commands in SQL? Give a description of their purpose.
Different DML commands in SQL: SELECT: retrieve or view data from the database INSERT: add new records to a table UPDATE: change existing records in a table DELETE: removes data from a table MERGE: performs an UPSERT operation, also known as insert or update. CALL: runs a PL/SQL procedure or Java prRead more
Different DML commands in SQL:
- SELECT: retrieve or view data from the database
- INSERT: add new records to a table
- UPDATE: change existing records in a table
- DELETE: removes data from a table
- MERGE: performs an UPSERT operation, also known as insert or update.
- CALL: runs a PL/SQL procedure or Java program
- EXPLAIN PLAN: explains the way the data is loaded
- LOCK TABLE: helps control concurrency
See lessWhat are the different DDL commands in SQL? Give a description of their purpose.
Different DDL commands in SQL: CREATE: creates objects in the database ALTER: makes changes to objects in the database DROP: removes objects from the database TRUNCATE: deletes all data from a table COMMENT: adds comments to the data dictionary RENAME: renames an object in the database
Different DDL commands in SQL:
- CREATE: creates objects in the database
- ALTER: makes changes to objects in the database
- DROP: removes objects from the database
- TRUNCATE: deletes all data from a table
- COMMENT: adds comments to the data dictionary
- RENAME: renames an object in the database
See less