• Introduction:

SQL is a powerful and widely used language for querying and manipulating data in relational databases. SQL stands for Structured Query Language and it allows you to perform various operations on data, such as selecting, inserting, updating, deleting, creating, altering and dropping tables, views, indexes and other database objects.

In this blog post, we will give you a brief overview of some of the basic topics of SQL that every SQL expert should know. These topics are:

1.  Data types: SQL supports different data types for storing different kinds of values in the database. Some of the common data types are: integer, decimal, varchar, date, time, boolean, etc. You can specify the data type of a column when you create a table or alter its definition.

2.  Constraints: Constraints are rules that enforce the integrity and validity of the data in the database. Some of the common constraints are: primary key, foreign key, unique, not null, check, default, etc. You can define constraints on columns or tables when you create or alter them.

3. Queries: Queries are statements that retrieve data from one or more tables or views in the database. You can use various clauses and keywords to filter, sort, group and join the data. Some of the common clauses and keywords are: select, from, where, order by, group by, having, join, etc.

4. Functions: Functions are predefined or user-defined routines that perform some calculations or operations on the data. SQL supports various types of functions, such as: aggregate functions (e.g., sum, count, avg), scalar functions (e.g., upper, lower, substring), date and time functions (e.g., current_date, date_part), etc.

5.  Subqueries: Subqueries are queries that are nested inside another query. They can be used to return a single value, a set of values or a table as an input to the outer query. Subqueries can be classified into two types: correlated and uncorrelated. Correlated subqueries depend on the values of the outer query and are executed for each row of the outer query. Uncorrelated subqueries do not depend on the values of the outer query and are executed only once.

6.  Transactions: Transactions are units of work that consist of one or more SQL statements that are executed as a single logical operation. Transactions ensure that the database remains consistent and reliable even in case of errors or failures. Transactions have four properties: atomicity (either all or none of the statements are executed), consistency (the database state is valid before and after the transaction), isolation (the transactions do not interfere with each other) and durability (the effects of the transactions are permanent).

 Conclusion

These are some of the basic topics of SQL that you should master if you want to become an SQL expert. Of course, there is much more to learn and practice in SQL than what I have covered in this blog post. I hope this post has given you a good introduction to SQL and motivated you to explore more about this fascinating language.