Condition in MySQL

Updated May 10, 2023

Introduction to Condition in MySQL

Condition in MySQL is an open-source RDBMS (Relational Database Management System) that uses a standard language SQL – Structured Query Language for manipulating, storing, and retrieving database records. In simple words, we can say that MYSQL is a Database server that is a fast, secure, and easy-to-use application for many small and big businesses and different purposes – Web Database, Data Warehousing, E-Commerce, Logging applications, and more.

A database encompasses one or multiple tables with rows and columns. A name represents each table, and SQL statements perform any action on a database. Here, we will discuss Conditional statements in MYSQL, which are based on some conditional expressions. An expression can be any arrangement of MySQL literals like variables, operators, and functions that, on execution, returns a logical value if the condition is satisfied.

Conditional Operators in MySQL

Let’s first view some of the important SQL statements with the syntax:

1. SELECT– extracts/selects records from a database. ‘*’ denotes ‘all’.

SELECT column1, column2,......  FROM table_name;
SELECT * FROM table_name;

2. UPDATE– updates existing fields in a database

UPDATE tablename SET col1 = value1, col2 = value2, ... WHERE condition;

3. DELETE– deletes records from a database

DELETE FROM table_name WHERE condition;

4. DROP DATABASE – Deletes database

DROP DATABASE database_name;

5. INSERT INTO– adds new records into the database

INSERT INTO name_of_table (col1,col2,   ...) VALUES (val1, val2, ...);

6. CREATE DATABASE– generates a new database

CREATE DATABASE databasename;

7. CREATE TABLE– generates a new table

CREATE TABLE tablename ( col1 datatype, col2 datatype, col3 datatype, .... );

8. ALTER TABLE– make changes to a table

ALTER TABLE table_name ADD column_name datatype;

9. DROP TABLE– removes a table

DROP TABLE table_name;

10. CREATE INDEX– produces an index (search key)

CREATE INDEX index_name ON table_name (column1, column2, ...);

11. DROP INDEX– removes an index

DROP INDEX index_name ON table_name;

1. SQL Arithmetic Operators

2. SQL Bitwise Operators

3. SQL Comparison Operators

4. SQL Logical Operators

5. Conditional Operators

You can learn and practice SQL queries from educba.com in a straightforward understanding way.

1. IF() Function

If the condition is TRUE result is “YES,” and if the condition is FALSE, then “NO”.

Syntax:

IF(condition, value_if_true, value_if_false)

SQL Statement: 

SELECT IF(400<2000, "YES", "NO");

Output:

2. COALESCE () Function

Results in the first non-null value in a list.

Syntax:

COALESCE (val1, val2, ...., val_n)

SQL Statement:

SELECT COALESCE (NULL, 1, 5, 'example.com');

Output:

3. CASE Function

Checks all the conditions, and if the first condition is met, returns a value and will not read further. If no conditions are fulfilled, then the value will be returned in the ELSE clause. But again, it will return NULL if no ELSE portion and no conditional expressions are true.

Syntax:

CASE
WHEN condition1 THEN result1
WHEN condition2 THEN result2
WHEN conditionN THEN resultN
ELSE result
END;

Suppose a table Customer:

SQL Statement:

SELECT CustomerID, CustomerName, Address FROM Customers
ORDER BY (CASE
WHEN Address IS NULL THEN  City
ELSE Address
END);

Output:

4. ISNULL () Function

Results 1 if the expression is NULL; otherwise, returns 0.

Syntax:

SELECT ISNULL (expr)

SQL Statement:

SELECT ISNULL (NULL);

Output:

SQL Statement:

SELECT ISNULL ("Hello!");

Output:

5. NULLIF () Function

If two expressions are equal on the comparison, then it returns NULL. Otherwise, if not, then the first expression is the result.

Syntax:

SELECT NULLIF (expr1, expr2)

SQL Statement:

SELECT NULLIF (30, 30);

Output: 

SQL Statement:

SELECT NULLIF (50, "Test");

Output:

6. IFNULL () Function

A particular value is returned if the expression is NULL; if NOT NULL, it returns the expression. Syntax:

SELECT IFNULL (expr, alt_value)

SQL Statement:

SELECT IFNULL (NULL, "Learning SQL");

Output: 

SQL Statement:

SELECT IFNULL ("100", "Database SQL");

Output: 

7. GREATEST

It results in the biggest value from a list of two or multiple terms. If any conditional expression in the list is NULL, it returns NULL.

Syntax:

SELECT GREATEST (expr1, expr2 [...])

SQL Statement:   

SELECT GREATEST(10, 35, 88, 55);

Output:

8. IN

Check whether a value is inside a set of given or listed values. We can use it with CHECK, WHERE, and creation of views.

Syntax:

WHERE column IN (y1, y2, y3 [...])

SQL Statement:

SELECT * FROM Customers WHERE city IN ('Bareilly', 'Katihar',’Delhi’);

Output:

9. LEAST

It provides the least value from the list of two or multiple expressions; the result will be NULL if there is a NULL value expression in the list.

Syntax:

SELECT LEAST (expr1, expr2 [, ...])

SQL Statement:     

SELECT LEAST (10, 35, 88, 55); Output:

Conclusion – Condition in MySQL

If we want to create a website that displays data from a database, we need to know the following:

• An RDBMS database platform such as MS Access, SQL Server, MySQL.
• PHP, ASP, Python, Java, Node.js, JavaScript-like server-side scripting languages.
• Query language SQL to access the records from the database we want to show on the webpage.
• Knowledge of HTML and CSS to elegance the page.

Generally, IFandCASE is the standard conditional statement used in MYSQL. These conditional operators have reduced using multiple OR conditions for SELECT, UPDATE, INSERT, or DELETE SQL statements. So, conditional operators in MYSQL are probably helpful for filtering the data and providing exact results based on certain conditions so that it saves our time and effort in fetching information from the database.

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