Database.Guide – Page 296

How to Drop a Foreign Key in SQLite

December 10, 2020 by Ian

Normally if you need to drop a foreign key in SQL, you’d use the ALTER TABLE statement. But if you’re using SQLite, that’s not an option.

SQLite DROP TABLE

December 10, 2020December 10, 2020 by Ian

In SQLite, you can drop a table with the DROP TABLE statement.

You can optionally add the IF EXISTS clause to suppress any errors that might occur if the table doesn’t exist.

Also, if the table is referenced by a foreign key, there are a few things to be aware of.

SQL DROP COLUMN for Beginners

December 10, 2020 by Ian

In SQL, if you want to remove a column from a table, you need to use the ALTER TABLE statement with the DROP COLUMN clause.

That removes the column and all its data.

SQL Tutorial for Beginners

February 18, 2021December 9, 2020 by Ian

In this SQL tutorial for beginners, you will create your own database, insert data into that database, and then run queries against that database.

This SQL tutorial will get you running SQL queries in no time!

How to Rename a Column in SQL

December 9, 2020 by Ian

This article provides a quick example of renaming a table in SQL.

Most of the major RDBMSs allow you to rename a column with the ALTER TABLE statement. SQL Server is an exception.

SQL ALTER TABLE for Beginners

December 9, 2020December 9, 2020 by Ian

In SQL, the ALTER TABLE statement modifies the definition of an existing table.

You can use ALTER TABLE to alter, add, or drop columns and constraints.

Depending on your DBMS, the ALTER TABLE statement can also be used to reassign and rebuild partitions, or disable and enable constraints and triggers.

SQL UNION Clause for Beginners

October 22, 2023December 8, 2020 by Ian

In SQL, the UNION clause concatenates the results of two queries into a single result set.

You can use the UNION clause with or without the ALL argument:

UNION ALL – Includes duplicates.
UNION – Excludes duplicates.

Some RDBMSs also accept UNION DISTINCT, which is the equivalent to UNION. That is, it excludes duplicates.

Below are some basic examples to demonstrate how it works.

SQL AVG() for Beginners

July 23, 2023December 8, 2020 by Ian

In SQL, the AVG() function is an aggregate function that returns the average of all values in a given expression.

It can also be used to return the average of all distinct (unique) values in an expression.

The expression must be numeric (it cannot be character string, bit string, or datetime).

Below are some basic examples to demonstrate how it works.

SQL SUM() for Beginners

July 23, 2023December 8, 2020 by Ian

In SQL, the SUM() function is an aggregate function that returns the sum of all values in a given expression.

It can also be used to return the sum of all distinct (unique) values in an expression.

The expression must be numeric (it cannot be character string, bit string, or datetime).

Below are some basic examples to demonstrate how it works.

SQL MAX() for Beginners

July 23, 2023December 7, 2020 by Ian

In SQL, the MAX() function is an aggregate function that returns the maximum value in a given expression.

Below are some basic examples to demonstrate how it works.