Even though PL/SQL and SQL are tightly integrated with each other, there are a number of differences in the way they operate. While SQL executes one query at once, PL/SQL can execute an entire block of code. SQL and PL/SQL also differ in their performances, error handling capabilities and the way they interact with databases. In this article, we will look at all the differences between the two languages so you know what their individual usages are.
SQL: Brief Overview
Structured Query Language (SQL) is a powerful, non-procedural, database language which is used in the management of relational databases. Developed by IBM research, it is highly portable, upgradeable and offers a high degree of abstraction when compared with procedural languages. Through SQL, end-users can interact with several database management systems as per their availability.
PL/SQL: Brief Overview
PL/SQL is a powerful procedural language that extends procedural constructs to SQL statements. It is known for its high processing speed and error handling capabilities.
In PL/SQL, blocks of code or multiple statements are executed at once which consist of functions, triggers, packages, etc, that enhance the functionality of an operation. This also helps in reducing network traffic. Learn more about PLSQL developer salary in India.
The block-structured language has program blocks that can be of two types:
- Anonymous Blocks – when a block of code is not stored in your database.
- Stored procedures – when a block is named and stored as a parsed representation in your database.
Must Read: SQL Developer Salary in India
Key Differences Between SQL and PL/SQL
- SQL is a Structural Query Language created to manipulate relational databases. It is a declarative, detail-oriented language. Whereas, PL/SQL is a Procedural Language/Structured Query Language that uses SQL as its database. It is an application-oriented language.
- There are no variables in SQL whereas PL/SQL has variables constraints, data types, etc.
- In SQL, we use DDL and DML to write queries and commands whereas with PL/SQL, code blocks containing functions, triggers, variables, control structures (for loop, while), conditional statements (if..then..else) are written.
- In SQL, a single operation or query can be executed at a time. However, In PL/SQL, multiple operations or an entire block of close can be executed at once. This results in reduced network traffic.
- It is possible to embed in a PL/SQL block whereas the opposite can’t be done.
- Unlike PL/SQL, there is direct interaction between SQL and the database server
- PL/SQL offers high processing speed while performing manipulation of large volumes of data. This can’t be achieved with SQL.
SQL vs PLSQL: Execution
Execution in SQL
We have statements in SQL which are essentially instructions through which a user tells SQL what they want to be done. SQL then compiles these instructions and navigates the database to perform the task.
Every operation needs to be executed using SQL statements. Further, there are certain words in SQL that are reserved to perform a specific task. For instance, SELECT, UPDATE, DELETE. These can not be used as names for any other purpose. (Note: Almost all operations are performed by SQL but there are also tools and apps available to make SQL’s task easier.)
There are six types of statements in SQL.
- Data Manipulation Language statements (DML)
- Data Definition Language statements (DDL)
- Transaction Control statements
- Session Control statements
- System Control statements
- Embedded SQL statements
Data Manipulation Language statements and Data Definition Language statements are most commonly used in SQL queries. So, let’s take a brief look at the two:
Data Manipulation Statements (DML)
DML statements comprise the likes of SELECT, DELETE, INSERT, UPDATE. They are basically used to manipulate a database. Using DML statements, you can perform operations like delete or add rows, select a particular table or more than one table, select a view, updates values in existing rows, etc.
Here is an example:
SELECT ename, mgr, comm + sal FROM emp;
INSERT INTO emp VALUES
(4321, ‘ROBERT’, ‘ACCOUNTANT’, 9876, ’14-JAN-1982′, 1600, 500, 30);
DELETE FROM emp WHERE ename IN (‘WARD’,’JONES’);
Data Definition Statements (DDL)
Using DDL statements, you can create a schema object, alter its structure or rename or drop it. You can also delete all the data in a schema object without having to delete the entire structure. There are several other operations that you can perform using DDL statements.
Some DDL statements include CREATE, ALTER, DROP, TRUNCATE, ANALYSE, COMMENT, to mention a few.
Here is an example:
CREATE TABLE plants
(COMMON_NAME VARCHAR2 (15), LATIN_NAME VARCHAR2 (40));
DROP TABLE plants;
GRANT SELECT ON emp TO Scott;
REVOKE DELETE ON emp FROM Scott;
Execution in PL/SQL
Procedures are stored in the database to be called as required by an application. They can also be called from another PL/SQL block (anonymous or stored). As a procedure is called by an application, it is compiled and loaded into the System Global Area where PL/SQL and SQL process them using their respective executors.
Every program unit a PL/SQL is present in the form of a block, which consists of declarations and statements. It can be nested to include another block.
They are designated by the following keywords
- DECLARE – for variables, subprograms and local types. A declarative part of a block ends on completion of execution to avoid clutter.
- BEGIN – contains statements which have access to the declarations. This is the executable part of the block.
- EXCEPTION – any exceptions raised during execution are taken care of here. The exception handling part of the block is usually placed at the end of a subprogram to eliminate exceptions in the same.
Another important aspect of PL/SQL is its control structures that help you control the flow of statements. These are quite important while writing Triggers.
They can be categorised into three types
- Conditional Control: This includes the IF-THEN-ELSE statements where if checks for a condition, ELSE indicates the action to perform and ELSE denotes what should be done if the condition is not true.
- Iterative Control: These include loop statements using which you can perform an action multiple times. FOR, WHILE and WHEN are included here.
- Sequential Control: This is to let you move from one label to another without any conditions applied. (GOTO statement)
Usage of SQL and PL/SQL
Due to the detail-oriented nature of SQL and that it can directly interact with the databases), SQL statements are a great option for creating analytical reports. Since it writes DML statements, it also finds use in supporting applications where there is a need for simple updating. Essentially, it is designed for data manipulation and does just that.
PL/SQL is application-based and is primarily used to design applications such as building user screens or creating back-end logic for web pages. SQL is responsible for providing data for these PL/SQL based applications. PL/SQL can be integrated with Java and PHP to create complex logic.
As we know, PL/SQL is an extension of SQL and does what SQL does but on large volumes of data using functions, control structures and triggers. SQL only deals with the what of action while PL/SQL even tells you how.
PL/SQL is a refined approach to deal with complex SQL problems. While SQL is better at data abstraction and portability, PL/SQL scores where performance and speed are concerned.
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Write about the subsets of the Structures Query Language?
There are four significant subsets of the Structured Query Language (SQL): Data Definition Language (DDL), Data Manipulation Language (DML), Data Control Language (DCL), Transaction Control Language (TCL). DDL defines the structure of the table in the relational database. It consists of commands like ALTER, CREATE, DROP, etc. DML is used to manipulate or update an existing database with commands like SELECT, INSERT, UPDATE, etc. DCL controls the access levels to the database by different users in the organization using GRANT and REVOKE. TCL deals with transactional operations like ROLLBACK, COMMIT, SAVEPOINT, etc. These languages help us to perform different complex operations on the relational database.
How a primary key is different from a foreign key?
The primary key in a database is used to ensure that the data in each tuple (row) is unique in the table. The foreign key in a database provides a link between two tables and points to the primary key of another table. A relational table can have only one primary key, whereas it can have multiple foreign keys. A primary key is a mixture of NOT NULL and unique constraints on the table. A foreign key can have duplicate values in the table. Foreign keys can also have NULL records, unlike primary keys. A primary key value can't be deleted from the parent table in the database, whereas a foreign key value in a database can be deleted from the child table.
Write about different types of SQL operations?
SQL operators are special characters reserved to perform certain operations, making it easy to write complex SQL queries. Arithmetic operators are used for mathematical calculations on the data in tables. Logical operators evaluate a given expression and return true or false by using ALL, ISNULL, EXISTS, BETWEEN, LIKE, etc. Comparison operators check the relation between two values using <, >, <=, >=, etc. Bitwise operators are used on integer type values to perform bit manipulations by using ~, |, ^, etc. Compound operators perform operations on a value before setting its variable’s value to the result using +=, -=, *=, /=, etc. String operators are used to perform concatenation and pattern matching for the values in the table.